Make sure sidebar panels are focused when open, and focus is restored when closed

[acelaya]

This PR requires hypothesis/frontend-shared#957
It is also a continuation of #5361, where some of the improvements suggested there have been applied.

This PR makes use of the new Dialog focusing capabilities, to make sure the sidebar panels are focused when opened, and the focus is restored once closed.

It's done in a way that the Slider transitions are kept, so it has no visual changes.

focus-and-transition.mp4

This PR also fixes hypothesis/product-backlog#1421

TODO

• Fix tests

Testing steps

1. First make sure your local frontend-shared is up to date. Then build it with make build, and "publish" it with npx yalc publish. Not needed anymore.
2. Clone this branch on your local client , and run npx yalc add @hypothesis/frontend-shared to install the version you published in previous step.
3. Use the keyboard to open sidebar panels ("share annotations" or "help" ones can be used for testing).
4. Check the focus behaves as expected, focusing the panel after the open transition has finished, and recovering focus to the button when close transition ends.

[codecov]

Codecov Report

Merging #5390 (52b7e70) into main (24813dc) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #5390   +/-   ##
=======================================
  Coverage   99.19%   99.19%           
=======================================
  Files         237      237           
  Lines        9403     9406    +3     
  Branches     2243     2244    +1     
=======================================
+ Hits         9327     9330    +3     
  Misses         76       76           

Impacted Files	Coverage Δ
src/sidebar/components/SidebarPanel.tsx	100.00% <100.00%> (ø)
src/sidebar/components/Slider.tsx	100.00% <100.00%> (ø)

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[lyzadanger]

👍🏻 🥳