Reverts * https://github.com/flutter/engine/pull/47454 and adds documentation The NDK folder shuffling in the DEPS is to simplify the build files and enable building with different NDK versions between Dart and Flutter while sharing the build files. Closes: https://github.com/flutter/flutter/issues/136666 [C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style