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

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

third_party/git/mergetools/xxdiff

@@ -0,0 +1,23 @@
+diff_cmd () {
+	"$merge_tool_path" \
+		-R 'Accel.Search: "Ctrl+F"' \
+		-R 'Accel.SearchForward: "Ctrl+G"' \
+		"$LOCAL" "$REMOTE"
+}
+
+merge_cmd () {
+	if $base_present
+	then
+		"$merge_tool_path" -X --show-merged-pane \
+			-R 'Accel.SaveAsMerged: "Ctrl+S"' \
+			-R 'Accel.Search: "Ctrl+F"' \
+			-R 'Accel.SearchForward: "Ctrl+G"' \
+			--merged-file "$MERGED" "$LOCAL" "$BASE" "$REMOTE"
+	else
+		"$merge_tool_path" -X $extra \
+			-R 'Accel.SaveAsMerged: "Ctrl+S"' \
+			-R 'Accel.Search: "Ctrl+F"' \
+			-R 'Accel.SearchForward: "Ctrl+G"' \
+			--merged-file "$MERGED" "$LOCAL" "$REMOTE"
+	fi
+}