Merge branch 'tb/pack-bitmap-write-cleanups'

The pack bitmap code saw some clean-up to prepare for a follow-up topic. * tb/pack-bitmap-write-cleanups: pack-bitmap: introduce `bitmap_writer_free()` pack-bitmap-write.c: avoid uninitialized 'write_as' field pack-bitmap: drop unused `max_bitmaps` parameter pack-bitmap: avoid use of static `bitmap_writer` pack-bitmap-write.c: move commit_positions into commit_pos fields object.h: add flags allocated by pack-bitmap.h