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.
diff --git a/src/edit.c b/src/edit.c
index 435e1ed..65c53f5 100644
--- a/src/edit.c
+++ b/src/edit.c
@@ -1177,6 +1177,7 @@
 	case K_LEFTDRAG:
 	case K_LEFTRELEASE:
 	case K_LEFTRELEASE_NM:
+	case K_MOUSEMOVE:
 	case K_MIDDLEMOUSE:
 	case K_MIDDLEDRAG:
 	case K_MIDDLERELEASE: