Merge branch 'ps/cat-file-filter-batch'

Merge branch 'ps/cat-file-filter-batch'

"git cat-file --batch" and friends learned to allow "--filter=" to
omit certain objects, just like the transport layer does.

* ps/cat-file-filter-batch:
  builtin/cat-file: use bitmaps to efficiently filter by object type
  builtin/cat-file: deduplicate logic to iterate over all objects
  pack-bitmap: introduce function to check whether a pack is bitmapped
  pack-bitmap: add function to iterate over filtered bitmapped objects
  pack-bitmap: allow passing payloads to `show_reachable_fn()`
  builtin/cat-file: support "object:type=" objects filter
  builtin/cat-file: support "blob:limit=" objects filter
  builtin/cat-file: support "blob:none" objects filter
  builtin/cat-file: wire up an option to filter objects
  builtin/cat-file: introduce function to report object status
  builtin/cat-file: rename variable that tracks usage