Add centralized ReservedPrimitiveTypes registry and shared toSafeIdentifier helper (#56049)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/56049

Reduce duplication and inconsistency across codegen generators by centralizing reserved primitive type mappings into a single `ReservedPrimitiveTypes.js` registry, making future type support and fixes a single-source change and lowering bug risk.

Additionally, standardize identifier capitalization via a shared `toSafeIdentifier` helper in `Utils.js` to prevent divergent string handling across C++/Java helpers.

Also removes dead TODO comments and obsolete commented-out code from `RNCodegen.js`, `GenerateModuleH.js`, and parser files.

Changelog: [Internal]

Reviewed By: alanleedev

Differential Revision: D95711348

fbshipit-source-id: 3f541f91f8dcc21e8e8b75cf2f0e402807d18f8a