Implement Structs in GDScript

[decryptedchaos]

This adds Structs to GDScript

Status

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Functional POC

Tasks:

Refactoring this to fit Godot's COW model. It shouldn't be anymore heavy than the Variant based Refcounted instance, and solve the fundamental issue.

This will need extensive debug, testing and cleanup. but is now functional

Summary by CodeRabbit

• New Features

  • Native GDScript struct support: declare fields/methods, inheritance, editor/analysis/compiler/VM/runtime integration, struct wrappers and copy-on-write instances, property listing, JSON/marshalling and bytecode support, and language-agnostic creation/inspection APIs.

• Breaking Changes

  • Removed legacy object-serialization utilities: var_to_str_with_objects and str_to_var_with_objects.

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