merge(third_party/git): Merge squashed git subtree at v2.23.0 r/373

Merge commit '1b593e1ea4d2af0f6444d9a7788d5d99abd6fde5' as 'third_party/git'

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diff --git a/third_party/git/Documentation/git-pack-refs.txt b/third_party/git/Documentation/git-pack-refs.txt
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+git-pack-refs(1)
+================
+
+NAME
+----
+git-pack-refs - Pack heads and tags for efficient repository access
+
+SYNOPSIS
+--------
+[verse]
+'git pack-refs' [--all] [--no-prune]
+
+DESCRIPTION
+-----------
+
+Traditionally, tips of branches and tags (collectively known as
+'refs') were stored one file per ref in a (sub)directory
+under `$GIT_DIR/refs`
+directory.  While many branch tips tend to be updated often,
+most tags and some branch tips are never updated.  When a
+repository has hundreds or thousands of tags, this
+one-file-per-ref format both wastes storage and hurts
+performance.
+
+This command is used to solve the storage and performance
+problem by storing the refs in a single file,
+`$GIT_DIR/packed-refs`.  When a ref is missing from the
+traditional `$GIT_DIR/refs` directory hierarchy, it is looked
+up in this
+file and used if found.
+
+Subsequent updates to branches always create new files under
+`$GIT_DIR/refs` directory hierarchy.
+
+A recommended practice to deal with a repository with too many
+refs is to pack its refs with `--all` once, and
+occasionally run `git pack-refs`.  Tags are by
+definition stationary and are not expected to change.  Branch
+heads will be packed with the initial `pack-refs --all`, but
+only the currently active branch heads will become unpacked,
+and the next `pack-refs` (without `--all`) will leave them
+unpacked.
+
+
+OPTIONS
+-------
+
+--all::
+
+The command by default packs all tags and refs that are already
+packed, and leaves other refs
+alone.  This is because branches are expected to be actively
+developed and packing their tips does not help performance.
+This option causes branch tips to be packed as well.  Useful for
+a repository with many branches of historical interests.
+
+--no-prune::
+
+The command usually removes loose refs under `$GIT_DIR/refs`
+hierarchy after packing them.  This option tells it not to.
+
+
+BUGS
+----
+
+Older documentation written before the packed-refs mechanism was
+introduced may still say things like ".git/refs/heads/<branch> file
+exists" when it means "branch <branch> exists".
+
+
+GIT
+---
+Part of the linkgit:git[1] suite