react-native-babel-preset: Add transform snapshot tests (#55338)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/55338

Add snapshot tests to validate Babel transform output under `react-native/babel-preset` under different configurations (default, hermes-stable, hermes-canary) and options (dev/prod, ESM output, babel-runtime). This enables catching unintended transform changes during preset updates.

The tests use a "kitchen-sink" input fixture covering private fields, async generators, Flow enums, JSX, hooks, and other syntax patterns, with separate output files per configuration for easy diffing.

Changelog: [Internal]

Reviewed By: vzaidman

Differential Revision: D91677590

fbshipit-source-id: d28becdd93a781004287dcd1889ac50224d2a91b