### Description
1. Fixing issues identified by similarity checker
2. Fix the corresponding sql unit tests
3. Fix JSTests failure due to above changes
4. Fix corresponding C# test failure
----
#### AI description (iteration 1)
#### PR Classification
This pull request is a code cleanup that standardizes and improves error message wording across the codebase.
#### PR Summary
The changes update error messages throughout the repository to provide clearer, more consistent, and more detailed feedback when operations fail.
- Updates in geospatial operator files (e.g. in `$geoNear`, `$near`, `$nearSphere`) replace informal phrasing with precise messages.
- Numerous error messages in aggregation and projection test files have been reworded for consistent phrasing
<!-- GitOpsUserAgent=GitOps.Apps.Server.pullrequestcopilot -->
### Does this PR have any customer impact?
Yes
### Type (Feature, Refactoring, Bugfix, DevOps, Testing, Perf, etc)
Feature
### Does it involve schema level changes? (Table, Column, Index, UDF, etc level changes)
Yes
### Are you introducing any new config? If yes, do you have tests with and without them being set?
Yes
### ChangeLog (Refer [Template](../oss/CHANGELOG.md))
### Description
Index hints are a mongo feature that allows customers to specify which index they would like to target for a query. Typically this is used in diagnostic scenarios when testing query performance.
With the new composite index op class coming in, we’re introducing side by side support for composite which makes it so we would want customers to be able to test which index is better for planning.
In this spirit, index hints is introduced which follows the same infra as the force pushdown for geonear and text and adds a new option for index hints.
As part of this the code is also refactored to cleanup some of the logic in the relpathlist and fix correctness issues around text index force pushdown (which was needed to handle index hints)
----
#### AI description (iteration 1)
#### PR Classification
This pull request introduces a new feature to support index hints in DocumentDB.
#### PR Summary
The changes integrate index hint support into query planning and execution, allowing users to force a specific index during query processing. Key updates include:
- **`src/opclass/index_support.c`**: Added new functions and a force index operator type (`ForceIndexOpType_IndexHint`) for filtering available indexes and generating custom operator expressions based on index hints.
- **`src/planner/documents_planner.c`**: Modified base table query planning logic to detect index hints and adjust index pushdown, including updates to path and restriction handling.
- New UDFs (e.g., `bson_dollar_index_hint`) and configuration variables (`EnableIndexHintSupport`, `UseLegacyForcePushdownBehavior`) were added to support the hint mechanism.
- Test files and SQL scripts (e.g., in `/oss/internal/pg_documentdb_distributed/src/test/regress/`) were introduced or updated to validate index hint pushdown behavior.
- Documentation and release notes (e.g., `docs/pgmongo/design_docs/data_plane/indexing/index_hints.md`, `pgmongo_1.106.md`, and `CHANGELOG.md`) were updated to describe the index hint feature.
<!-- GitOpsUserAgent=GitOps.Apps.Server.pullrequestcopilot -->
### Does this PR have any customer impact?
Not yet
### Type (Feature, Refactoring, Bugfix, DevOps, Testing, Perf, etc)
Feature/POC
### Does it involve schema level changes? (Table, Column, Index, UDF, etc level changes)
Yes
### Are you introducing any new config? If yes, do you have tests with and without them being set?
No
### ChangeLog (Refer [Template](../oss/CHANGELOG.md))
### Description
This adds more changes for orderby support in the index
1) Fixes the correctness issue arising from indexing arrays for order by - we remove the top level array term from indexing. To handle this, we move the query operators to support querying the index correctly when the query is on an array
2) For `$elemMatch` this temporarily makes elemMatch just a full scan for now (a subsequent change wil tackle updating the logic)
3) Adds orderby to the top level schema for the internal extension
4) For exists false/true, we were pushing a lot more terms to the runtime recheck. Ensure that we're hitting the right index terms and evaluate correctly against the index.
----
#### AI description (iteration 1)
#### PR Classification
This pull request is a code cleanup and enhancement that removes array term generation for composite indexes and updates related index term handling.
#### PR Summary
The changes streamline composite index generation by eliminating dedicated array terms, and they adjust boundary, metadata, and recheck logic to ensure consistent behavior. Key updates include:
- **`oss/pg_documentdb/src/opclass/bson_gin_composite_core.c`**: Removed redundant array term generation and introduced functions like `SetArrayEqualityBound` to properly handle equality bounds for arrays.
- **`oss/pg_documentdb/src/opclass/gin_index_term.c`**: Updated index term serialization and metadata management (including handling of undefined values via `GenerateValueUndefinedTerm`) to align with the new composite index behavior.
- **Test and expected output files**: Revised expected composite index term outputs and SQL tests to reflect the removal of array-specific terms.
- **Documentation and configuration**: Updated design docs and removed the configuration flag for skipping array term generation, consolidating the new composite index strategy.
<!-- GitOpsUserAgent=GitOps.Apps.Server.pullrequestcopilot -->
### Does this PR have any customer impact?
No
### Type (Feature, Refactoring, Bugfix, DevOps, Testing, Perf, etc)
Refactor
### Does it involve schema level changes? (Table, Column, Index, UDF, etc level changes)
No
### Are you introducing any new config? If yes, do you have tests with and without them being set?
No
### Release Note (Refer [Template](../docs/release_notes/pgmongo_template.md))
### Description
Move source files not pertinent to OSS out of OSS
----
#### AI description (iteration 1)
#### PR Classification
Code cleanup
#### PR Summary
This pull request moves source files not pertinent to OSS out of the OSS directory and includes some code refactoring.
- Moved `rum_custom_join_scan.c` and `external_configs.c` from `pg_documentdb` to `pg_helio_api`.
- Added `IsValidScanPath` function and refactored path validation in `custom_scan_continuation.c`.
- Introduced `TryOptimizePathForBitmapAnd` function in `api_hooks.c` and updated related hooks.
- Added new external configuration variables in `documentdb_init.c`.
- Removed `RegisterRumJoinScanNodes` from `pg_documentdb` and added it to `pgmongo` and `pg_helio_api`.
### Does this PR have any customer impact?
No
### Type (Feature, Refactoring, Bugfix, DevOps, Testing, Perf, etc)
Refactoring
### Does it involve schema level changes? (Table, Column, Index, UDF, etc level changes)
No
### Are you introducing any new config? If yes, do you have tests with and without them being set?
No
### Release Note (Refer [Template](../docs/release_notes/pgmongo_template.md))
### Description
Remove helio references from documentdb
Remove helio references from documentdb_distributed
----
#### AI description (iteration 1)
#### PR Classification
Code cleanup
#### PR Summary
This pull request removes references to "helio" and replaces them with "documentdb" in the sources of `documentdb` and `documentdb_distributed`.
- `metadata_cache.h` and `metadata_cache.c`: Replaced "Helio" with "DocumentDB" in variable names and function names.
- `pgmongo.c`: Updated include statements and function calls to use "documentdb" instead of "helio".
- `planner.c`: Updated planner function and related calls to use "DocumentDBApiPlanner".
- Moved several header files from `helio_*` to `documentdb_*` naming convention without code changes.
- `commands_common.c` and `create_indexes.c`: Updated function calls and variable names to use "DocumentDB" instead of "Helio".
### Does this PR have any customer impact?
No
### Type (Feature, Refactoring, Bugfix, DevOps, Testing, Perf, etc)
Refactor
### Does it involve schema level changes? (Table, Column, Index, UDF, etc level changes)
No
### Are you introducing any new config? If yes, do you have tests with and without them being set?
No
### Release Note (Refer [Template](../docs/release_notes/pgmongo_template.md))
### Description
Move source files under new directory.
----
#### AI description (iteration 1)
#### PR Classification
Code reorganization
#### PR Summary
This pull request moves the `helio_api` and `helio_distributed` sources under the `documentdb` directory, updating references and initialization logic accordingly.
- Added `pg_documentdb.c` for initializing the `pg_documentdb` extension.
- Added `documentdb_distributed.c` for initializing the `pg_documentdb_distributed` extension.
- Updated `validate_helio_extension_state.sh` to include new checks for `documentdb`.
- Moved `helio_api_extension_version.c` to `documentdb_extension_version.c` without code changes.
- Updated various `Makefile` configurations to reflect the new directory structure and dependencies.
Jinrui Zhang
Vinod Sridharan
Zinan Ren