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

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

third_party/git/Documentation/RelNotes/2.0.2.txt

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+Git v2.0.2 Release Notes
+========================
+
+ * Documentation for "git submodule sync" forgot to say that the subcommand
+   can take the "--recursive" option.
+
+ * Mishandling of patterns in .gitignore that has trailing SPs quoted
+   with backslashes (e.g. ones that end with "\ ") have been
+   corrected.
+
+ * Recent updates to "git repack" started to duplicate objects that
+   are in packfiles marked with .keep flag into the new packfile by
+   mistake.
+
+ * "git clone -b brefs/tags/bar" would have mistakenly thought we were
+   following a single tag, even though it was a name of the branch,
+   because it incorrectly used strstr().
+
+ * "%G" (nothing after G) is an invalid pretty format specifier, but
+   the parser did not notice it as garbage.
+
+ * Code to avoid adding the same alternate object store twice was
+   subtly broken for a long time, but nobody seems to have noticed.
+
+ * A handful of code paths had to read the commit object more than
+   once when showing header fields that are usually not parsed.  The
+   internal data structure to keep track of the contents of the commit
+   object has been updated to reduce the need for this double-reading,
+   and to allow the caller find the length of the object.
+
+ * During "git rebase --merge", a conflicted patch could not be
+   skipped with "--skip" if the next one also conflicted.