- Add "stub" sourceset to each subproject
- Directly pass vararg sourcesets to methods in PlatformExtension to
  avoid automatically shipping jars with the api stubs
- We may have to include stubs in setupLoomMod, but I don't think so
- A lot of this can be stripped back out if we don't need stub sources
  for the forge/fabric subprojects

- Add Sodium 0.6 and Iris API stubs to stubs source set and remove Gradle dependencies on local Sodium jar, Iris, and Oculus
- Ensure usage of APIs that may not exist at runtime is in private classes and access is always guarded
- Change ShadersModHandler
  - Rename to ShadersModHelper
  - Convert methods to check for Iris' and Optifine's presence into static final fields
  - Move implementation to impl source set in form of IrisCompat and OptifineCompat classes
- Rename CompatMods to CompatMod and add public field to access mod ID
- Set BlockEntityType's Sodium predicate to null after it is removed
- Update repository links
- Remove local libs repository