Aria - alertdialog implementation

[jonasdd]

alertdialog design pattern is not fully implemented. The design pattern is nearly the same of dialog design patten, only assistive technologies interpretation is not the same.

Like a dialog, alertdialog must :

• have a focustrap 👍
• set focus to a focusable element inside a modal 👍 . Focus is always set to the next button. A nice feature should be, to give the choice where the focus is set on dialog opening
• modal have a title 👎 . The component needs to allow to pass aria-label or aria-labbelledby attribute. aria-labelledby take an id that should be passed to the title element <h2>
• once closed, focus is set back to the button that did open the dialog or to an other element in a more natural workflow. 👍

Also, if the modal is mounted at the very beginning or end of DOM, the title inside the dialog should likely be an <h1> rather than an <h2> because and there is very little chance there will be an <h1> element as parent (this will lead to a W3C error)