patch 8.1.1548: popup_dialog() is not implemented

Problem:    Popup_dialog() is not implemented.
Solution:   Implement popup_dialog() and popup_filter_yesno().
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 544426f..d371c28 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -815,6 +815,8 @@
     {"popup_clear",	0, 0, f_popup_clear},
     {"popup_close",	1, 2, f_popup_close},
     {"popup_create",	2, 2, f_popup_create},
+    {"popup_dialog",	2, 2, f_popup_dialog},
+    {"popup_filter_yesno", 2, 2, f_popup_filter_yesno},
     {"popup_getoptions", 1, 1, f_popup_getoptions},
     {"popup_getpos",	1, 1, f_popup_getpos},
     {"popup_hide",	1, 1, f_popup_hide},