feat: add potion_has and potion_level (close #66)

src/main/java/com/extendedclip/papi/expansion/player/PlayerExpansion.java

@@ -447,6 +447,21 @@ public final class PlayerExpansion extends PlaceholderExpansion implements Confi
                 return bool(p.isLeashed());
             case "is_inside_vehicle":
                 return bool(p.isInsideVehicle());
+            case "potion_has": {
+                final PotionEffectType potion = PotionEffectType.getByName(identifier.replace("potion_has_", ""));
+                return bool(potion != null && p.hasPotionEffect(potion));
+            }
+
+            case "potion_level": {
+                final PotionEffectType potion = PotionEffectType.getByName(identifier.replace("potion_level_", ""));
+
+                if (potion == null || !p.hasPotionEffect(potion)) {
+                    return "0";
+                }
+
+                //noinspection DataFlowIssue
+                return String.valueOf(p.getPotionEffect(potion).getAmplifier());
+            }
         }
         // return null for unknown placeholders
         return null;