replaceInFile is listed as a platform-independent directive, but it looks like it's not implemented on Android.

I'm working on a manifest entry for a more involved RN module: react-native-gesture-handler, which needs edits to the ReactActivityDelegate class definition (https://kmagiera.github.io/react-native-gesture-handler/docs/getting-started.html).

File replacement is not necessarily the best way to do this, but it is a very powerful directive that unlocks a lot of possibilities.

I have an initial implementation here: https://github.com/electrode-io/electrode-native/compare/master...runtrizapps:feature/android-replace-in-file?expand=1

Worth noting: I'm performing the replacements after the mustache templates are evaluated, which may differ from the approach on iOS (it seems like replaceInFile is designed to process incoming plugin files, not the final container files).

Perhaps a container transformer would be more appropriate? Not sure if there is a way to link a manifest-plugin entry with a container transformation..

Not submitting a PR at this time: just want to hear thoughts/rationale from the team. Happy to refactor or try out different approaches.

Thank you!