Merge branch 'ps/object-store-cleanup'

Merge branch 'ps/object-store-cleanup'

Further code clean-up in the object-store layer.

* ps/object-store-cleanup:
  object-store: drop `repo_has_object_file()`
  treewide: convert users of `repo_has_object_file()` to `has_object()`
  object-store: allow fetching objects via `has_object()`
  object-store: move function declarations to their respective subsystems
  object-store: move and rename `odb_pack_keep()`
  object-store: drop `loose_object_path()`
  object-store: move `struct packed_git` into "packfile.h"