Add context to no-noninteractive-tabindex on when this might be valid

[backwardok]

There's a use case for adding tabindex="0" to a generic container (like a <div>) to add keyboard accessibility to a scrollable container. Without the tabindex attribute, if the scrollable container doesn't contain any interactive elements, you won't be able to scroll that content with a keyboard.

Since there's no role associated with this, there isn't really anything to key off of to determine that this shouldn't be checked. The only current workaround for this is to disable the rule for that line.

[backwardok]

BTW I thought about adding something to this when I was updating all the docs today, but I wasn't super sure what the recommendation should be.

[kr8n3r]

yep, long code block wrapped in pre. tabindexgoes on thepre` element

[eps1lon]

PR up over at #760.