Fallback to SyntaxTree formatting if RuboCop is not used by the application

[vinistock]

If a project does not use RuboCop, we can still fallback and offer auto-formatting through SyntaxTree. The interface used to format the file was introduced here.

As a part of this work, investigate if the best solution is to remove rubocop from our dependencies, check if it's a part of the application's bundle and then decide which auto-formatting to use.

Alternatively, we can keep rubocop as a dependency and check for a .rubocop.yml file.