DEV: extract leave_group method from the group#remove_member method (#13823)

* Copy remove_member to new `leave` method

* Remove unneeded code from the leave method

* Rearrange the leave method

* Remove unneeded code from the remove_member method

* Add tests

* Implement on the client side

app/controllers/groups_controller.rb

@@ -464,7 +464,7 @@ class GroupsController < ApplicationController
   def remove_member
     group = Group.find_by(id: params[:id])
     raise Discourse::NotFound unless group
-    group.public_exit ? ensure_logged_in : guardian.ensure_can_edit!(group)
+    guardian.ensure_can_edit!(group)
 
     # Maintain backwards compatibility
     params[:usernames] = params[:username] if params[:username].present?
@@ -475,16 +475,6 @@ class GroupsController < ApplicationController
       'user_ids or usernames or user_emails must be present'
     ) if users.empty?
 
-    if group.public_exit
-      if !guardian.can_log_group_changes?(group) && current_user != users.first
-        raise Discourse::InvalidAccess
-      end
-
-      unless current_user.staff?
-        RateLimiter.new(current_user, "public_group_membership", 3, 1.minute).performed!
-      end
-    end
-
     removed_users = []
     skipped_users = []
 
@@ -507,6 +497,21 @@ class GroupsController < ApplicationController
     )
   end
 
+  def leave
+    ensure_logged_in
+    unless current_user.staff?
+      RateLimiter.new(current_user, "public_group_membership", 3, 1.minute).performed!
+    end
+
+    group = Group.find_by(id: params[:id])
+    raise Discourse::NotFound unless group
+    raise Discourse::InvalidAccess unless group.public_exit
+
+    if group.remove(current_user)
+      GroupActionLogger.new(current_user, group).log_remove_user_from_group(current_user)
+    end
+  end
+
   MAX_NOTIFIED_OWNERS ||= 20
 
   def request_membership