patch 8.1.1406: popup_hide() and popup_show() not implemented yet

Problem:    popup_hide() and popup_show() not implemented yet.
Solution:   Implement the functions.
diff --git a/src/proto/popupwin.pro b/src/proto/popupwin.pro
index 172c079..64fca5f 100644
--- a/src/proto/popupwin.pro
+++ b/src/proto/popupwin.pro
@@ -1,6 +1,9 @@
 /* popupwin.c */
 void f_popup_create(typval_T *argvars, typval_T *rettv);
+int popup_any_visible(void);
 void f_popup_close(typval_T *argvars, typval_T *rettv);
+void f_popup_hide(typval_T *argvars, typval_T *rettv);
+void f_popup_show(typval_T *argvars, typval_T *rettv);
 void popup_close(int id);
 void popup_close_tabpage(tabpage_T *tp, int id);
 void close_all_popups(void);