Focusing a customizer control from the preview should show the controls on mobile

[celloexpressions]

When shift-clicking on a partial in the preview, we now open the controls pane if it was collapsed as of #36678. Similarly, on mobile we should show the controls pane when a control is focused from the preview. This is of course not something users will commonly run into currently, since shift-click typically isn't available on small-screen devices; however, it will be necessary for things like #27403 to work.

This should be fixed similarly to #36678, potentially by leveraging the same paneVisible value on mobile when the controls are toggled.

[westonruter]

Perhaps the an equally cross theme-compatible to shift-click on mobile devices is long press. The problem with that, however, is there is no tooltip that would show as when hovering is done.

[celloexpressions]

Yeah, I think if we can fix the bug with not opening the controls pane here, the actual UI can be worked out in #27403.

[celloexpressions]

We have visible edit icons now, so we definitely need this in 4.7. Are you working on a patch @seancjones?

[seancjones]

Yes, I have time this weekend and I plan to take care of it then if not sooner.

[seancjones]

Unified Customizer behavior on small/mobile and large views.

[seancjones]

That should do it. There's an added benefit of the state of the Preview Pane being the same between small and large screens, so toggling hide/show panel will be the same in an expanded and contracted window.

[westonruter]

Add full path in diff and add spacing

[westonruter]

In 39010:

Customize: Reveal controls pane when clicking on edit shortcuts in mobile preview.

Re-use paneVisible state to also manage whether the mobile preview-only class is applied to the overlay.

Props seancjones.
See #36678, #36678, #27403.
Fixes #38080.

[westonruter]

@seancjones excellent work. It's actually fun to use the customizer on mobile now!