Merge branch 'ps/odb-drop-whence'

The 'whence' field in 'struct object_info' has been removed. The backend-specific object information retrieval has been refactored into an opt-in 'struct object_info_source' structure. * ps/odb-drop-whence: odb: document object info fields odb: drop `whence` field from object info treewide: convert users of `whence` to the new source field odb: add `source` field to struct object_info_source odb: make backend-specific fields optional packfile: thread odb_source_packed through packed_object_info()