Update project documentation

[tobrun]

Ticket tracking project documentation changes for /platform/android
The current .MD files in our repository for Android our outdated and we need to addmore usefull information for debugging, building and distributing .so and .aar files:

• Update documentation with Android IDE integration from Integrate CMake build into Gradle + Android Studio #8363
• Cleanup old wiki pages
• Review build requirements
• Cleanup CONTRIBUTING.MD
• Update test/run documentation in MapboxGLAndroidSDKTestApp
• update make android-help - command with other targets
• add make android-help to documentation
• update ndk-stack documentation
• Update distributing with .aar section, apk split and abi filter configuration
  • add link to: https://github.com/mapbox/mapbox-gl-native/wiki/Strategies-to-reduce-Android-APK-size.
• Add information about style spec changes and code generation
• Update release documentation with Circle CI information
• Make checkstyle setup discoverable / part of getting started

[tobrun]

Added a section in OP, to update release documentation related to CircleCI migration (more specifcally about changing CircleCI config to build a release + changing the config to original state afterwards).

[zugaldia]

cc: @langsmith @cammace to help support the effort.

[cammace]

Also noting here (not sure if ticketed) that all public methods need to have the corresponding javadoc.

[tobrun]

Parts of this issue should still be picked up before a final 5.1.0 release (for this reason, keeping it to this milestone). After fixes have landed we can move this to a 5.2.0 milestone (though it would be great to resolve all the todo's).

[zugaldia]

Parts of this issue should still be picked up before a final 5.1.0 release (for this reason, keeping it to this milestone).

What work is left (if any) for the current 5.1?

[tobrun]

the javadoc was the missing part, that is fixed with #9266, moving to next milestone for now.

[tobrun]

NDK stack documentation has been updated here to reflect changes in our build system (the .so files are found in a different place).

[zugaldia]

@tobrun Looks like all items in OP are now checked, are we good to close?

[tobrun]

#9788 is targeting to close this, so once CI approves and PR is merged, this will be closed ;)