We don't use that info for anything, and it generates unnecessary diffs
every time we bump the minor version (and CI failures if we forget to
sync some files from opt-in modules (mono, text_server_fb).
* Placeholder textures
* Placeholder meshes
* Placeholder material
This PR is the first step towards implementing https://github.com/godotengine/godot-proposals/issues/2756
It adds an asset type that uses no resources, which can be used to replace the existing ones on export for using on the upcoming server export.
