Internalise RNTester examples referencing unexported APIs (#51019)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/51019

Follows D72228547 and D73770609.

This diff internalises (moves files from fbsource+GitHub to fbsource only) a number of RNTester examples which referenced `'react-native/src/private/'` subpaths.

In future, new components/APIs should be exported from index as `unstable_`, or added to `RNTesterListFbInternal` if they are exported from `src/fb_internal/`.

Changelog: [Internal]

Reviewed By: cortinico

Differential Revision: D73777092

fbshipit-source-id: d9fb0833c56f2ae580b6db62ddbbbeae774a0004