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

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

third_party/git/Documentation/RelNotes/1.7.2.2.txt

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+Git v1.7.2.2 Release Notes
+==========================
+
+Fixes since v1.7.2.1
+--------------------
+
+ * Object transfer over smart http transport deadlocked the client when
+   the remote HTTP server returned a failure, instead of erroring it out.
+
+ * git-gui honors custom textconv filters when showing diff and blame;
+
+ * git diff --relative=subdir (without the necessary trailing /) did not
+   work well;
+
+ * "git diff-files -p --submodule" was recently broken;
+
+ * "git checkout -b n ':/token'" did not work;
+
+ * "git index-pack" (hence "git fetch/clone/pull/push") enabled the object
+   replacement machinery by mistake (it never should have);
+
+And other minor fixes and documentation updates.