patch 8.1.1645: cannot use a popup window for a balloon

Problem:    Cannot use a popup window for a balloon.
Solution:   Add popup_beval().  Add the "mousemoved" property.  Add the
            screenpos() function.
diff --git a/src/normal.c b/src/normal.c
index 5c9f929..f626f45 100644
--- a/src/normal.c
+++ b/src/normal.c
@@ -2329,6 +2329,9 @@
 	    bevalexpr_due_set = TRUE;
 	}
 #endif
+#ifdef FEAT_TEXT_PROP
+	popup_handle_mouse_moved();
+#endif
 	return FALSE;
     }