Scroll to first highlighted annotation when loaded

[acelaya]

Part of #6255

This PR updates ThereadList so that it scrolls to the first highlighted annotation once pending updates have been loaded, as long as the user does not have any draft.

This is a simple approach to scroll into just-loaded annotations, however, we should probably scroll into the closest one based on the active scroll. I will try to address that separately.

Testing steps

1. Open http://localhost:3000 in two browsers
2. Make sure there's enough annotations so that the sidebar renders a scrollbar.
3. Scroll the sidebar to the very top or bottom in one browser.
4. Create or edit one or more annotations in the opposite edge of the sidebar, in the second browser.
5. Click the "load pending updates" notification in the first browser. You should get scrolled into the first one of those annotations.

If you do the same while editing/creaating an annotation, the scrolling should not happen, unless you cancel all drafts before the 5-second timeout where annotations are highlighted, is finished.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.43%. Comparing base (f261f95) to head (2c27fd8).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6337   +/-   ##
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  Coverage   99.43%   99.43%           
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  Files         271      271           
  Lines       10217    10223    +6     
  Branches     2419     2420    +1     
=======================================
+ Hits        10159    10165    +6     
  Misses         58       58           

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[robertknight]

This doesn't take account of the current sort order in the thread list. I guess it will scroll to whichever update came in first, if that is the order in which highlights naturally are sorted in the store?

One easy way to make this feel predictable might be to sort by last update time and scroll to the oldest (ie. the first update the user hasn't seen yet) or alternatively the newest.

[acelaya]

The only intention here was to make sure the user sees at least one of the highlighted annotations, without worrying too much which one is it.

But we could definitely pick one by date, as that should not complicate this too much.

[acelaya]

I started with an algorithm where scrolling happens to the first highlighted annotation, because it was a pretty simple logic to implement.

[robertknight]

LGTM. One issue I noticed in testing is that although the UI will scroll if needed, it won't switch tabs from annotations <-> notes or vice-versa. I suggest filing a follow-up issue for that.