In PR #20887 the issue got fixed partly, but two issues remained that
unintendedly left room for intermittent failres:
- in the "Ctrl+ArrowLeft/Right" loop the `waitForBrowserTrip` call was
placed _before_ the actual keypresses, which means that for the final
iteration of the loop the last key presses were not properly awaited;
- in the "ArrowLeft/ArrowRight" loop the `waitForBrowserTrip` call was
absent, which means that we didn't wait for key presses at all.
This commit fixes the issues by consistently waiting to a browser trip
_after_ each key press to make sure the sidebar got a chance to render.
This solves [bug 1989406](https://bugzilla.mozilla.org/show_bug.cgi?id=1989406).
(“The user should be able to dismiss the in-content message displayed by clicking somewhere else in the PDF”)
There’s a good gif there that shows the problematic behavior.
In the thread, there are also mentions of 2 similar but slightly separate problems:
* clicking on another highlight should also dismiss
* the mention that hitting the escape key does not dismiss
I found the last point, the escape key, to work already (first test case here).
But this PR solves the main bug (second test case) and the adjacent one
(third test case).
It works by using the existing `unselectAll` handling.
This really isn't necessary, and it's just a left-over from before the code was moved into the current file.
Also, spotted during rebasing, use the existing "locale" hash-parameter in integration-tests rather than adding a duplicate one for testing.
For now its use is limited to the comment sidebar but it'll be used for the new one
containing the thumbnails.
And make the sidebar more accessible with the keyboard or a screen reader.
