patch 8.1.1520: popup windows are ignored when dealing with mouse position

Problem:    Popup windows are ignored when dealing with mouse position
Solution:   Find the mouse position inside a popup window.  Allow for modeless
            selection.
diff --git a/src/proto/popupwin.pro b/src/proto/popupwin.pro
index 2a377a7..a274446 100644
--- a/src/proto/popupwin.pro
+++ b/src/proto/popupwin.pro
@@ -1,4 +1,6 @@
 /* popupwin.c */
+int popup_height(win_T *wp);
+int popup_width(win_T *wp);
 void popup_adjust_position(win_T *wp);
 void f_popup_clear(typval_T *argvars, typval_T *rettv);
 void f_popup_create(typval_T *argvars, typval_T *rettv);