patch 8.2.0748: cannot get a list of all popups

Problem:    Cannot get a list of all popups.
Solution:   Add popup_list().  Use it in the test runner.
diff --git a/src/evalfunc.c b/src/evalfunc.c
index c010116..c499890 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -715,6 +715,7 @@
     {"popup_getoptions", 1, 1, FEARG_1,	  ret_dict_any,	PROP_FUNC(f_popup_getoptions)},
     {"popup_getpos",	1, 1, FEARG_1,	  ret_dict_any,	PROP_FUNC(f_popup_getpos)},
     {"popup_hide",	1, 1, FEARG_1,	  ret_void,	PROP_FUNC(f_popup_hide)},
+    {"popup_list",	0, 0, 0,	  ret_list_number, PROP_FUNC(f_popup_list)},
     {"popup_locate",	2, 2, 0,	  ret_number,	PROP_FUNC(f_popup_locate)},
     {"popup_menu",	2, 2, FEARG_1,	  ret_number,	PROP_FUNC(f_popup_menu)},
     {"popup_move",	2, 2, FEARG_1,	  ret_void,	PROP_FUNC(f_popup_move)},