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

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

third_party/git/range-diff.h

@@ -0,0 +1,17 @@
+#ifndef RANGE_DIFF_H
+#define RANGE_DIFF_H
+
+#include "diff.h"
+
+#define RANGE_DIFF_CREATION_FACTOR_DEFAULT 60
+
+/*
+ * Compare series of commmits in RANGE1 and RANGE2, and emit to the
+ * standard output.  NULL can be passed to DIFFOPT to use the built-in
+ * default.
+ */
+int show_range_diff(const char *range1, const char *range2,
+		    int creation_factor, int dual_color,
+		    struct diff_options *diffopt);
+
+#endif