patch 8.0.0693: no terminal emulator support

Problem:    No terminal emulator support.  Cannot properly run commands in the
            GUI.  Cannot run a job interactively with an ssh connection.
Solution:   Very early implementation of the :terminal command.  Includes
            libvterm converted to ANSI C.  Many parts still missing.
diff --git a/src/libvterm/t/90vttest_02-screen-3.test b/src/libvterm/t/90vttest_02-screen-3.test
new file mode 100644
index 0000000..8cdf8df
--- /dev/null
+++ b/src/libvterm/t/90vttest_02-screen-3.test
@@ -0,0 +1,16 @@
+# Origin mode
+INIT
+WANTSCREEN
+
+RESET
+
+PUSH "\e[?6h"
+PUSH "\e[23;24r"
+PUSH "\n"
+PUSH "Bottom"
+PUSH "\e[1;1H"
+PUSH "Above"
+
+!Output
+?screen_row 22 = "Above"
+?screen_row 23 = "Bottom"