Add an alternative way to provide an accessibleName for Dialog

[jessegreenberg]

RIght now, the accessibleName is always provided as an h1. But that is not a 1:1 match with the visual. Sometimes we want an aria-label instead of a heading.

What if we added something like

accessibleNameConfiguration: 'heading' | 'label'

that would control the accessible name behavior.

[jessegreenberg]

@terracoda will read over some documentation and make sure this is good. Feel free to assign back to me when ready to implement.

[jessegreenberg]

OK, we discussed and this is good to go, I will add it.

[jessegreenberg]

This was added. @terracoda would you like to review how this sounds in context, or can this be closed?