fix: expose ShowInSearch field in access UI

Upgrading from SilverStripe 3 to SilverStripe 5 it appears the ShowInSearch field is no longer displayed in the UI.

The File record still contains this data and the implementation was to match Page instances which contain the 'Show in search' option to CMS editors.

code/Forms/AssetFormFactory.php

@@ -9,6 +9,7 @@
 use SilverStripe\Core\Config\Configurable;
 use SilverStripe\Core\Extensible;
 use SilverStripe\Core\Injector\Injectable;
+use SilverStripe\Forms\CheckboxField;
 use SilverStripe\Forms\FieldGroup;
 use SilverStripe\Forms\FieldList;
 use SilverStripe\Forms\Form;
@@ -370,7 +371,7 @@ protected function getFormFieldSecurityTab($record, $context = [])
         unset($editorsOptionsField[InheritedPermissions::ANYONE]);
         $membersMap = Member::get()->map('ID', 'Name');
 
-        return Tab::create(
+        $tab = Tab::create(
             'Permissions',
             OptionsetField::create(
                 'CanViewType',
@@ -401,6 +402,17 @@ protected function getFormFieldSecurityTab($record, $context = [])
                 $membersMap
             )
         );
+
+        if ($record instanceof File) {
+            $tab->push(
+                CheckboxField::create(
+                    'ShowInSearch',
+                    _t(__CLASS__.'.SHOWINSEARRCH', 'Show in search?')
+                )
+            );
+        }
+
+        return $tab;
     }
 
     public function getRequiredContext()