Scroll to the first new reply when the user chooses to show new replies

[daprice]

Pitch

1. I open the detail/conversation view of a post that has a lot of replies.
2. The “New replies available” toast appears.
3. I click “Show” on that toast.

Currently, the new replies are inserted into a mysterious location in the conversation that may be hidden from view, so it often appears that nothing happened when I click “Show”. I then have to infer (from experience that a new Mastodon user would not have) that it must have inserted them out of view, then scroll up and down through the thread hunting for the new replies while trying to remember which ones I have and haven’t seen.

Instead, clicking “Show” should scroll to the first of the newly shown replies or there should be a “scroll to new reply/replies” button in the toast after the new replies are loaded.

Since there may be multiple new replies strewn throughout the conversation and not all together, a highlight like what was suggested in #37245 would also be very helpful here.

Motivation

As a user, when I click a button labeled “Show”, I need the software to show me the effect of pressing that button, not make a change offscreen where I can’t see it.