f0ed60a2a517b687987cc68320b067d7d76998f6
shell/platform/android IDE-friendly, and add documentation (flutter/engine#49612)
Closes https://github.com/flutter/flutter/issues/141043. Nothing in this change should impact: - End-user apps - Testing and/or CI I've added what I believe is the minimum required to get a reasonable Android Studio experience with the `shell/platform/android` folder. More could definitely be done, but this unblocks me (i.e. https://github.com/flutter/flutter/issues/139702) and adds instructions for the next person. _I'm open to suggestions on how to improve this further, but unless they are critical, I'd rather land this as-is and review your PRs tweaking my documentation further (I have limited time to work exclusively on docs)._ --- Example after this: 
Description
Languages
Dart
75.4%
C++
16.4%
Objective-C++
2.7%
Java
2.7%
Objective-C
0.6%
Other
1.8%