patch 8.1.1875: cannot get size and position of the popup menu

Problem:    Cannot get size and position of the popup menu.
Solution:   Add pum_getpos(). (Ben Jackson, closes #4827)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index f117563..8943093 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -234,6 +234,7 @@
 #endif
 static void f_prevnonblank(typval_T *argvars, typval_T *rettv);
 static void f_printf(typval_T *argvars, typval_T *rettv);
+static void f_pum_getpos(typval_T *argvars, typval_T *rettv);
 static void f_pumvisible(typval_T *argvars, typval_T *rettv);
 #ifdef FEAT_PYTHON3
 static void f_py3eval(typval_T *argvars, typval_T *rettv);
@@ -741,6 +742,7 @@
     {"prop_type_get",	1, 2, 0,	  f_prop_type_get},
     {"prop_type_list",	0, 1, 0,	  f_prop_type_list},
 #endif
+    {"pum_getpos",	0, 0, 0,	  f_pum_getpos},
     {"pumvisible",	0, 0, 0,	  f_pumvisible},
 #ifdef FEAT_PYTHON3
     {"py3eval",		1, 1, 0,	  f_py3eval},
@@ -7961,6 +7963,19 @@
 }
 
 /*
+ * "pum_getpos()" function
+ */
+    static void
+f_pum_getpos(typval_T *argvars UNUSED, typval_T *rettv UNUSED)
+{
+    if (rettv_dict_alloc(rettv) != OK)
+	return;
+#ifdef FEAT_INS_EXPAND
+    pum_set_event_info(rettv->vval.v_dict);
+#endif
+}
+
+/*
  * "pumvisible()" function
  */
     static void