reverseRemapJar
private fun reverseRemapJar(input: Path, out: Path, provider: IMappingProvider, ignoreFieldDesc: Boolean, tag: String)
Whole-tree reverse remap into the compile-only mojmap symbol jar at out; shared by the fabric and forge branches, which differ only in provider and ignoreFieldDesc (TSRG2 fields carry no descriptor) — tag labels the timing log. input is a loader view, not a file, so it is the union's whole class tree and all supers resolve internally; ignoreConflicts absorbs forge-style override divergence.