a11y: support fallback aria roles

[TorstenDittmann]

Describe the problem

Right now, multiple aria roles separated by space on the same element will throw a a11y-unknown-role warning.

For example, role="row button" will throw a warning for the unknown role row button - but should actually validate row and button individually.

The role attribute is a set of space separated tokens. If the first token is not accessibility supported (or valid), the next one will be used for determining the semantic role of the element, and so forth.

References:

• https://www.w3.org/TR/2014/REC-wai-aria-20140320/host_languages#host_general_role
• https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#space-separated-tokens

Describe the proposed solution

Before checking the value, we can value.split(...) and check the values individually.

I would be more than happy to work on a PR 👍🏻

Alternatives considered

The alternative right now, is to add <!-- svelte-ignore a11y-unknown-role --> if you find yourself in this situation.

Importance

would make my life easier

[Conduitry]

This should be available now in 3.54.0 - thank you!