The display of New Message Line can be controlled by show-new-messages-divider

[smitea]

Describe the feature

When I noticed in Google Chat, the new message line is displayed like this

1. When a new message arrives, open the room and the new message line will be displayed

2. When the room is opened for the second time, the new message line will disappear

As far as I know, in the code, show-new-messages-divider can only control whether unread messages need to be added to newMessages, and when I can't externally control how to clear newMessages

Describe the solution

I hope to add a watcher of showNewMessagesDivider in Room.vue, and clear newMessages when the new value of showNewMessagesDivider is false, so that users can keep the original business while also using their own business to handle how to display/disappear new message line