[llvm][DebugInfo] Bump DWARFListTable maximum DWARF version (#183859)
Bumps `.debug_rnglists` maximum supported version to DWARFv6.
This does not mean we officially support DWARFv6. It just enables us
testing the features gradually.
Added unit-test since there was no prior test in the entire LLVM
test-suite that checked this.