Merge branch 'ps/object-store-midx-dedup-info'

Further code clean-up for multi-pack-index code paths. * ps/object-store-midx-dedup-info: midx: compute paths via their source midx: stop duplicating info redundant with its owning source midx: write multi-pack indices via their source midx: load multi-pack indices via their source midx: drop redundant `struct repository` parameter odb: simplify calling `link_alt_odb_entry()` odb: return newly created in-memory sources odb: consistently use "dir" to refer to alternate's directory odb: allow `odb_find_source()` to fail odb: store locality in object database sources