zink: more descriptor refactoring
requested to merge zmike/mesa:zink-descriptor_refactoring_part_four_this_one_is_pretty_good_but_not_even_my_final_form into main
- more work to abstract the current descriptor manager
- also make the api a bit more coherent in the process
- more code consolidation
- milestone: descriptor synchronization is now done during bind and then automatically as-needed