pack-objects: integrate --path-walk and some --filter options#2101

derrickstolee wants to merge 10 commits intogitgitgadget:en/backfill-fixes-and-edgesgitgitgadget/git:en/backfill-fixes-and-edgesfrom

derrickstolee:path-walk-filtersderrickstolee/git:path-walk-filtersCopy head branch name to clipboard