Rename viewDiscussions => viewForum, viewUserList => searchUsers (#2854)

This naming is clearer as to the intended effect. Changes include:

- A migration to rename all permissions
- Updating the seed migration to use the original naming from the start
- Replacing usage of the old names with new names in code
- Throwing warnings when the old names are used.

src/User/Access/ScopeUserVisibility.php

@@ -20,7 +20,7 @@ class ScopeUserVisibility
      */
     public function __invoke(User $actor, $query)
     {
-        if ($actor->cannot('viewDiscussions')) {
+        if ($actor->cannot('viewForum')) {
             if ($actor->isGuest()) {
                 $query->whereRaw('FALSE');
             } else {

src/User/User.php

@@ -404,6 +404,15 @@ class User extends AbstractModel
         return false;
     }
 
+    private function checkForDeprecatedPermissions($permission)
+    {
+        foreach (['viewDiscussions', 'viewUserList'] as $deprecated) {
+            if (strpos($permission, $deprecated) !== false) {
+                trigger_error('The `viewDiscussions` and `viewUserList` permissions have been renamed to `viewForum` and `searchUsers` respectively. Please use those instead.', E_USER_DEPRECATED);
+            }
+        }
+    }
+
     /**
      * Get the notification types that should be alerted to this user, according
      * to their preferences.