[feat] add a11y check on abstract roles

[anthonylegoas]

This PR adds an accessibility check on abstract roles. See the wai-aria 1.1 specification for more informations. #820

Before submitting the PR, please make sure you do the following

• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

Tests

• Run the tests with npm test and lint the project with npm run lint

[anthonylegoas]

I rebased the branch on master.
@benmccann Is there any chance for this PR to be merged?

[benmccann]

I'm really not the person to ask since I'm not that familiar with the Svelte core codebase or acessibility. Perhaps @geoffrich could take a peek at some point?

[Conduitry]

This has been released in 3.50.0. Thank you!