Modal - Add content for elementToFocus prop in a11y docs

[thatblindgeye]

Is this a new page or a change to an existing one?
Modal a11y docs

Describe the enhancement
We should add content in the a11y docs related to the elementToFocus prop introduced in React, which allows customizing what receives focus when the Modal is opened + what should typically receive focus.

Any other information?

[dlabaj]

Do you know what the docs would be? Also do you have a timeline on when we want to get this in.

[thatblindgeye]

Essentially either the first focusable+least destructive element, or the main text content if the Modal has a lot of content to the point that the first focusable element is out of view on initial open. https://www.w3.org/WAI/ARIA/apg/patterns/dialog-modal/examples/dialog/ has some guidelines that we can use for inspiration.

Q1 would be a nice to have, but getting it in for Q2 would be fine since it's just a docs update.