- Add MIME definitions for resources, scenes and scripts
- Remove the "weight" property, which defaults to 50, a much saner value than the previous 100, which was a bit excessive.
- Changes their icon names in order to follow the XDG icon naming conventions.
(cherry picked from commit 876e165a49)
Mime type definitions are usually named like the mime type they define,
i.e. x-godot-project in our case.
It was introduced with reverse DNS naming as that's what FlatHub favors,
so it will need to be renamed there.
