Serialize dictionaries adding newlines between key-value pairs
Serialize group lists also with newlines in between
Serialize string properties escaping only " and \ (needed for a good diff experience with built-in scripts and shaders)
Bonus:
Make AnimationPlayer serialize its blend times always sorted so their order is predictable in the .tscn file.
This PR is back-compat; won't break the load of existing files.
Cherry-picked from 7dbb1c0571
888f8b31e7