patch 8.1.1517: when a popup changes all windows are redrawn

Problem:    When a popup changes all windows are redrawn.
Solution:   Only update the lines that were affected.  Add a file for
            profiling popup windows efficiency.
diff --git a/src/popupwin.c b/src/popupwin.c
index c512369..3781c6f 100644
--- a/src/popupwin.c
+++ b/src/popupwin.c
@@ -571,8 +571,7 @@
 	    || org_width != wp->w_width
 	    || org_height != wp->w_height)
     {
-	// TODO: redraw only windows that were below the popup.
-	redraw_all_later(NOT_VALID);
+	redraw_all_later(VALID);
 	popup_mask_refresh = TRUE;
     }
 }