We used to include the raw jGui source in our jar and then had the main remapJar
task remap both of them to intermediary. This however does not work properly
when jGui needs additional mapping (e.g. because of mixin), resulting in
non-remapped mixins with fail to apply at runtime.
With this commit, we no longer include jGui in our raw jar and instead now have
shadowJar depend on jGui's remapJar task.
14b84c5e1b