Old Android Stuio versions pior to 2.2.0 didn't come with Java bundled. Make sure flutter doesn't crash when we try to determine the Java version of those old Android Studio installations.
It's not just $HOME/.AndroidStudio2.2, it might also be
.AndroidStudioPreview2.3, or .AndroidStudioFooBar1.7, or whatever.
Made the Version parser less throw-happy, and relaxed the directory name
checks to allow for the above.
Fixes#8353.
* Fix bug parsing Gradle version.
Version from pub_semver requires versions of the format X.Y.Z. Gradle
doesn't follow semantic versioning, though, so version parsing would
fail on versions like '3.2'. Fixed by writing a custom Version class.
Also removed a check for apksigner when building Gradle-based projects.
Fixes#8298
* Teach flutter tools to find gradle
Flutter tools will now use Gradle from Android Studio, which is now found automatically.
flutter doctor will verify that Android Studio has been installed, and that the included Gradle is at least version 2.14.1.
It is still possible to manually configure the path to Android Studio (flutter config --android-studio-dir=XXX) or Gradle (flutter config --gradle-dir=XXX), but this should only be necessary if they're installed somewhere non-standard.
Only tested on Linux and macOS for now.
Fixes#8131
