ManyToOne filter should not display ManyToOneHelper valueForm when exposed

Problem/Motivation

#2335659: Remove FormState ArrayAccess usage from core broke this so ManyToOneHelper valueForm is shown when a ManyToOne filter is exposed.

+++ b/core/modules/views/src/Plugin/views/filter/ManyToOne.php
@@ -111,7 +111,7 @@ function operators() {
-    if (empty($form_state['exposed'])) {
+    if ($form_state->get('exposed')) {

E.g. if this is checked and you try to reset the exposed form filters, you will get a redirect loop.

Proposed resolution

Fix it

Remaining tasks

User interface changes

No more:

API changes

None