2.0 dialog axe compliant

[kontrollanten]

Successor of https://github.com/prateekbh/preact-material-components/pull/1289

Before we merge this. From MDN:

• Each
  should be identified, typically by including a heading (<h1>-<h6> element) as a child of the

  element.
• Do not use the
  element as a generic container; this is what <div> is for, especially when the sectioning is only for styling purposes. A rule of thumb is that a section should logically appear in the outline of a document.

But that's just opinions (?), while the specs says that aria-role alertdialog must only be on dialog or section elements, so I guess that's the heaviest part.

[cromefire]

A rule of thumb is that a section should logically appear in the outline of a document.

Well that's given (sort of)

[cromefire]

Thanks!