Clean up versioning shenanigans involving LoaderVersion and QuiltMappingsVersion

[EnnuiL]

The separator and build fields were big mistakes and they should be rectified;
Quilt Loader never really fit into that paradigm due to it following SemVer and instead, these two fields should be replaced with a stable field akin to what GameVersion has, with SemVer being used to detect non-stable releases;
Now as for Quilt Mappings, separator should still be removed, but extra care should be taken for replacing the build field, especially since the Quilt Mappings versioning scheme is weird and with QM v2 in the plans, it's likely it can end changing to something unrecognizable
Finally, I believe we can drop the hashed field for QuiltMappingsVersionV4, we can add it back later if it ends being necessary (example: Tiny v3 happens and a JSON object would be needed), at least if it can be added back later