[process] Establish Java/Kotlin coding standards

For Dart contributions, we can point folks to the [Dart style guide](https://dart.dev/guides/language/effective-dart) as a North star (while flutter has [it's own](https://github.com/flutter/flutter/blob/master/docs/contributing/Style-guide-for-Flutter-repo.md)). We should establish what we want to do for Java/Kotlin and communicate that in the PR template and Contributing guides as well. (See: #8062).

See also: https://github.com/microsoft/vscode/wiki/Coding-Guidelines