Merge branch 'ps/packfile-store' into tb/incremental-midx-part-3.1

* ps/packfile-store: packfile: refactor `get_packed_git_mru()` to work on packfile store packfile: refactor `get_all_packs()` to work on packfile store packfile: refactor `get_packed_git()` to work on packfile store packfile: move `get_multi_pack_index()` into "midx.c" packfile: introduce function to load and add packfiles packfile: refactor `install_packed_git()` to work on packfile store packfile: split up responsibilities of `reprepare_packed_git()` packfile: refactor `prepare_packed_git()` to work on packfile store packfile: reorder functions to avoid function declaration odb: move kept cache into `struct packfile_store` odb: move MRU list of packfiles into `struct packfile_store` odb: move packfile map into `struct packfile_store` odb: move initialization bit into `struct packfile_store` odb: move list of packfiles into `struct packfile_store` packfile: introduce a new `struct packfile_store`