patch 8.2.1177: terminal2 test sometimes hangs in the GUI

Problem:    Terminal2 test sometimes hangs in the GUI.
Solution:   Move some tests to other files to further locate the problem.
            Set the GUI to a fixed screen size.
diff --git a/src/testdir/Make_all.mak b/src/testdir/Make_all.mak
index 12aeffe..d517667 100644
--- a/src/testdir/Make_all.mak
+++ b/src/testdir/Make_all.mak
@@ -272,6 +272,7 @@
 	test_termencoding \
 	test_terminal \
 	test_terminal2 \
+	test_terminal3 \
 	test_terminal_fail \
 	test_textformat \
 	test_textobjects \
@@ -488,6 +489,7 @@
 	test_termencoding.res \
 	test_terminal.res \
 	test_terminal2.res \
+	test_terminal3.res \
 	test_terminal_fail.res \
 	test_textformat.res \
 	test_textobjects.res \