docs: Update GML_REFERENCE.md

[EttyKitty]

Summary by cubic

Reorganized and expanded docs/GML_REFERENCE.md to clarify core GML concepts, improve the JS comparison, and add a full guide to method binding. This makes the reference easier to scan and more accurate for everyday use.

• Refactors
  • Moved “Comparison: GML vs JavaScript” to the top and made it GML-first.
  • Added “Asset Types” (Scripts, Objects, events, inheritance, built-ins).
  • Expanded “Methods and Binding” with implicit methods, method() binding, static struct quirks, and examples.
  • Clarified array copy‑on‑write and accessors ([@] vs normal indexing) with a practical example.
  • Updated legacy DS structures; added ds_stack, ds_queue, ds_priority; noted required ds_destroy().
  • Split and renamed sections: “Built‑in Functions List” and “Keywords List” (with preprocessor directives).

^{Written for commit 156b49b. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 1 file

Confidence score: 5/5

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_{Re-trigger cubic}