patch 8.1.1136: decoding of mouse click escape sequence is not tested

Problem:    Decoding of mouse click escape sequence is not tested.
Solution:   Add a test for xterm and SGR using low-level input.  Make
            low-level input execution with feedkeys() work.
diff --git a/src/testdir/Make_all.mak b/src/testdir/Make_all.mak
index 81d0dc7..97cd166 100644
--- a/src/testdir/Make_all.mak
+++ b/src/testdir/Make_all.mak
@@ -250,6 +250,7 @@
 	test_taglist \
 	test_tcl \
 	test_termencoding \
+	test_termcodes \
 	test_terminal \
 	test_terminal_fail \
 	test_textformat \
@@ -402,6 +403,7 @@
 	test_tab.res \
 	test_tcl.res \
 	test_termencoding.res \
+	test_termcodes.res \
 	test_terminal.res \
 	test_terminal_fail.res \
 	test_textformat.res \