We have upstreamed two patches for git-fetch(1) which speed up mirror
fetches in repositories with hundreds of millions of references. The
first patch makes better use of the commit-graph when computing common
objects, and the second patch will cause us to skip computing the output
width when fetching with the `--quiet` flag.

The patches were tested with our notorious problem repo `www-gitlab-com`
with speedups of about 25% when doing mirror-fetches.

Backport them into our own Git version now that they have been merged
via 2b331293fb (Merge branch 'ps/fetch-optim-with-commit-graph' into
next, 2022-02-14).

Changelog: performance