[issue2551321] make pre examples in docs pages tabable

New submission from John Rouillard:

Currently keyboard users can't select and scroll the example pre sections in the docs.
For example on https://roundup-tracker.org/docs/security.html#index-1 there is a yellow 
scrollable pre box. It can't be selected/tabbed to and can't be scrolled by the keyboard.

Firefox allows the region to get focus via tab and be scrolled using the arrow keys.
Also cursor mode (F7) allows the user to move the cursor along the line an scrolls when he 
cursor goes out of the box. Chrome implemented it and then rolled it back. Safari has yet to
implement.

https://adrianroselli.com/2022/06/keyboard-only-scrolling-areas.html

suggests adding: tabindex=0 aria-label/aria-labeledby and role=region or possibly role=group.
Role region is a landmark role, so the scrollable box can show up in a region browser like the 
main or navigation roles. I don't like that. However it is interactive so it apparently
needs a role.

I am not sure if Sphinx can be convinced to generate the proper output though.

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components: Documentation
messages: 7953
nosy: rouilj
severity: normal
status: new
title: make pre examples in docs pages tabable
type: behavior

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Roundup tracker <[email protected]>
<https://issues.roundup-tracker.org/issue2551321>
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