patch 8.0.1309: cannot use 'balloonexpr' in a terminal

Problem:    Cannot use 'balloonexpr' in a terminal.
Solution:   Add 'balloonevalterm' and add code to handle mouse movements in a
            terminal. Initial implementation for Unix with GUI.

src/ex_getln.c

@@ -1452,6 +1452,7 @@ getcmdline(
 	case K_X2MOUSE:
 	case K_X2DRAG:
 	case K_X2RELEASE:
+	case K_MOUSEMOVE:
 		goto cmdline_not_changed;
 
 #endif	/* FEAT_MOUSE */