Fix random crashes during GC.

This switches from the (apparently deprecated) WeakCallbackData-based SetWeak() to the newer WeakCallbackInfo-based one.

I have no fucking idea what the difference is, or what the WeakCallbackType enum is supposed to mean, or why it didn't work before. There is no documentation. There are various pages around the internet that make reference to this API but no comprehensive explanation anywhere as to the details. You're supposed to just know, or something.

src/node-capnp/capnp.cc

@@ -853,7 +853,8 @@ public:
     obj->SetAlignedPointerInInternalField(0, const_cast<std::type_info*>(&typeid(T)));
     obj->SetAlignedPointerInInternalField(1, ptr);
     v8::Persistent<v8::Object>(v8::Isolate::GetCurrent(), obj)
-        .SetWeak(reinterpret_cast<void*>(ptr), deleteAttachment<T>);
+        .SetWeak(reinterpret_cast<void*>(ptr), deleteAttachment<T>,
+                 v8::WeakCallbackType::kParameter);
     return obj;
   }
 
@@ -896,7 +897,7 @@ private:
   std::unordered_map<std::type_index, OwnHandle<v8::FunctionTemplate>> templates;
 
   template <typename T>
-  static void deleteAttachment(const v8::WeakCallbackData<v8::Object, void>& data) {
+  static void deleteAttachment(const v8::WeakCallbackInfo<void>& data) {
     delete reinterpret_cast<T*>(data.GetParameter());
   }
 };
@@ -1808,7 +1809,7 @@ void fromBytes(const v8::FunctionCallbackInfo<v8::Value>& args) {
       if (reinterpret_cast<uintptr_t>(buffer.begin()) % sizeof(capnp::word) != 0) {
         // Array is not aligned.  We have to make a copy.  :(
         auto array = kj::heapArray<capnp::word>(buffer.size() / sizeof(capnp::word));
-        memcpy(array.begin(), buffer.begin(), buffer.size());
+        memcpy(array.begin(), buffer.begin(), array.asBytes().size());
         words = array;
         bufferHandle = context.wrapper.wrapCopy(kj::mv(array));
       } else {