patch 8.1.1422: popup_getoptions() not implemented yet

Problem:    Popup_getoptions() not implemented yet.
Solution:   Implement it. (closes #4452)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 2abbcfe..7753fc6 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -811,6 +811,7 @@
 #ifdef FEAT_TEXT_PROP
     {"popup_close",	1, 1, f_popup_close},
     {"popup_create",	2, 2, f_popup_create},
+    {"popup_getoptions", 1, 1, f_popup_getoptions},
     {"popup_getposition", 1, 1, f_popup_getposition},
     {"popup_hide",	1, 1, f_popup_hide},
     {"popup_move",	2, 2, f_popup_move},