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

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/Documentation/git-mktree.txt

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+git-mktree(1)
+=============
+
+NAME
+----
+git-mktree - Build a tree-object from ls-tree formatted text
+
+
+SYNOPSIS
+--------
+[verse]
+'git mktree' [-z] [--missing] [--batch]
+
+DESCRIPTION
+-----------
+Reads standard input in non-recursive `ls-tree` output format, and creates
+a tree object.  The order of the tree entries is normalized by mktree so
+pre-sorting the input is not required.  The object name of the tree object
+built is written to the standard output.
+
+OPTIONS
+-------
+-z::
+	Read the NUL-terminated `ls-tree -z` output instead.
+
+--missing::
+	Allow missing objects.  The default behaviour (without this option)
+	is to verify that each tree entry's sha1 identifies an existing
+	object.  This option has no effect on the treatment of gitlink entries
+	(aka "submodules") which are always allowed to be missing.
+
+--batch::
+	Allow building of more than one tree object before exiting.  Each
+	tree is separated by as single blank line. The final new-line is
+	optional.  Note - if the `-z` option is used, lines are terminated
+	with NUL.
+
+GIT
+---
+Part of the linkgit:git[1] suite