Only use hidden until-found in panels if browsers supports it

[lb-]

• fixes hidden="until-found" usage broken in browsers lacking support #8961
• Note: There may be a different fix for this (CSS only) but this seemed the quickest way to get to the goal of the panels closing / opening correctly by using feature detection for this + as browsers upgrade they will automatically get the new behaviour.
• Tested on Chrome, Firefox and Safari - all now correctly collapse the panels, but Chrome still has the ability to search in the page to find content within collapsed items.

[lb-]

@gasman as Thibaud may be away this week I was not sure if he would get a chance to do a fix so I just did my best fix for now I could think of so the RC is not blocked.

We can maybe find a different fix during the RC process if needed.

cc @thibaudcolas

[squash-labs]

Manage this branch in Squash

Test this branch here: https://fix8961-use-hidden-until-found-961bk.squash.io

[gasman]

Happy with this fix - works well in Firefox and is consistent with the fallback suggested on https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/hidden . (It strikes me as a little odd that caniuse.com links to https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/hidden as the canonical reference, but that page doesn't actually explain until-found at all - ah well!)

Will hold off merging until tomorrow in case @thibaudcolas has any strong feelings against it, but if not I think this is good to go.

[thibaudcolas]

Thank you @lb-! I’ll review this later today. I would have thought it would be the styling that’s off rather than the JS logic for this, but if I got this wrong then we can merge this as-is.

[lb-]

@thibaudcolas yeah I agree there is probably a styling solution for this but when I looked at it - it was not immediately obvious. Hence, I went with the recommended approach from the chrome dev docs for feature detection instead.

[thibaudcolas]

Merging this as-is as I don’t think I’ll have the time to review this properly!

[lb-]

Thanks Thibaud

[helenb]

(It strikes me as a little odd that caniuse.com links to https://developer.mozilla.org/en-> US/docs/Web/HTML/Global_attributes/hidden as the canonical reference, but that page doesn't actually explain until-> found at all - ah well!)

I just noticed that exact issue (reviewing this code as I'm going to be doing some work on a global expand / contract button) - I've reported it on the MDN repo now.