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/evalfunc.c b/src/evalfunc.c
index 2d796f7..3af5cd7 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -5870,6 +5870,9 @@
 #ifdef FEAT_TERMGUICOLORS
 	"termguicolors",
 #endif
+#ifdef FEAT_TERMINAL
+	"terminal",
+#endif
 #ifdef TERMINFO
 	"terminfo",
 #endif