Lower generators in Hermes development profiles

[OskarEichler]

Summary:

Hermes stable/canary development profiles intend to lower generators for debugger compatibility, but enableRegenerator is currently passed only to @babel/plugin-transform-runtime. That replaces runtime references but does not lower generator syntax, so dev output still contains native function* declarations.

Run @babel/plugin-transform-regenerator explicitly for those development profiles. Async and destructuring preservation experiments take precedence: standalone regenerator otherwise overrides preserved async syntax and crashes on generator-local destructuring when runtime helpers are disabled.

Changelog:

[INTERNAL] [FIXED] - Lower generators in Hermes development profiles while respecting syntax-preservation experiments.

Test Plan:

• Added a stable-dev regression proving a generator is lowered and uses @babel/runtime/regenerator; exact baseline retains function*.
• Added no-runtime regressions proving explicit async/destructuring preservation remains intact and no longer crashes.
• Regenerated the four affected dev fixtures through the repository's snapshot update path; preserve-async/destructuring fixtures remain unchanged.
• Full preset Jest passes: 4/4 suites, 113/113 tests, 16 snapshots.
• Fresh Flow check reports 0 errors; targeted no-ignore ESLint, Prettier, and git diff --check pass.
• An exhaustive 384-combination profile/dev/preservation/runtime/module matrix leaves no regenerator/destructuring failures.

Compatibility / breaking changes

Development transform output intentionally changes to match the preset's existing debugger-compatibility policy. Production output and explicit async/destructuring preservation behavior are unchanged; there is no public API break.