BuiltinMethods

Caches ptrcall function pointers for builtin-type methods (Array.size, Dictionary.keys, ...). Resolving one requires the type, a StringName of the method, and the method's hash from extension_api.json; the resulting function pointer is stable for the process, so it is memoized.

This is the builtin-type analogue of the engine-class method binding Phase 2 will generate; it is kept minimal here to support the Phase 1 containers.