Summary:
- The version check that ensures the JS and native versions match is now in its own module for two reasons: it is easier to test and it allows react-native-windows to override just this module to implement its own version check (ex: more advanced checks for RNW-specific code).
- Added unit tests for the version checking to specify its behavior more clearly, including parity between dev and prod to avoid prod-only behavior and mitigate SEVs.
- Prefixed the Obj-C `#define` with `RCT_` to conform with other RN globals.
Closes https://github.com/facebook/react-native/pull/16403
Differential Revision: D6068491
Pulled By: hramos
fbshipit-source-id: 2b255b93982fb9d1b655fc62cb17b126bd5a939a
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