Inline the last duplicate Platform.select key

[OskarEichler]

Summary:

The React Native Babel preset statically replaces Platform.select({...}) for the target platform. Its property scan currently stops at the first matching key, while JavaScript object-literal evaluation keeps the last duplicate definition. For example, Platform.select({ios: 1, ios: 2}) runs as 2 but the preset compiles it to 1.

Scan the already-validated static properties from the end so compiled output matches runtime semantics while preserving O(n), allocation-free lookup. Metro has a parallel transform that can run first; companion Metro PR #1889 applies the same correction so output remains transform-order independent.

Changelog:

[GENERAL] [FIXED] - Inline the last duplicate key from static Platform.select object literals.

Test Plan:

• Added a focused preset regression; pristine main emits const value=1, while the fix emits const value=2.
• Full preset Jest passes: 4/4 suites, 111/111 tests, 16 snapshots.
• Fresh Flow check reports 0 errors.
• Targeted no-ignore ESLint, Prettier, and git diff --check pass.

No behavior changes for object literals without duplicate static keys; no UI change.