Move engine checkout to repo_utils module.

This is going to help us to implement the functionality once and reuse
in all the recipes.

Change-Id: I59e86dc78d1245e773b15fd42722c007c60a8e35
Bug: https://github.com/flutter/flutter/issues/59337
Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/3606
Reviewed-by: Keyong Han <keyonghan@google.com>
Commit-Queue: Godofredo Contreras <godofredoc@google.com>