Flutter migration: Build system update

[Izchomatik]

roc-droid Flutter migration child issue.

Restore original gradle features

• Build properties
  • compileSdk, minSdkVersion, targetSdkVersion
  • ndk version
  • jvm version
  • app versionName & versionCode - load from AndroidManifest.xml or from flutter
• Android manifest
  • AndroidManifest.xml should have hard-coded version and version code, and build system should automatically update them
  • permissions (see also here)
  • intents
  • service
• APK building
  • add project version to APK file name (roc-droid-1.2.3.apk)
• APK signing
  • sign locally
  • sign on CI
• Display app version in flutter
  • add package_info_plus, it should load version from AndroidManifest
  • use it in AboutPage
• Spotless
  • gradle targets to run spotless (check & format)
  • doit targets
• tag.py
  • move version-related stuff (compute, update, check version) from tag.py to gradle or flutter or dodo.py
  • move tag-related stuff (creating and pushing tag) from tag.py to dodo.py
  • remove tag.py