patch 8.2.1978: making a mapping work in all modes is complicated

Problem:    Making a mapping work in all modes is complicated.
Solution:   Add the <Cmd> special key. (Yegappan Lakshmanan, closes #7282,
            closes 4784, based on patch by Bjorn Linse)
diff --git a/src/insexpand.c b/src/insexpand.c
index 7e61e61..eebf01d 100644
--- a/src/insexpand.c
+++ b/src/insexpand.c
@@ -1822,7 +1822,7 @@
 
     // Ignore end of Select mode mapping and mouse scroll buttons.
     if (c == K_SELECT || c == K_MOUSEDOWN || c == K_MOUSEUP
-	    || c == K_MOUSELEFT || c == K_MOUSERIGHT)
+	    || c == K_MOUSELEFT || c == K_MOUSERIGHT || c == K_COMMAND)
 	return retval;
 
 #ifdef FEAT_PROP_POPUP