The BlockBreadcrumb shouldn't be a NavigableToolbar

[afercia]

The BlockBreadcrumb component added in #5658 is wrapped in a NavigableToolbar component.

Seems to me this is not appropriate because:

• NavigableToolbar adds arrows navigation via NavigableMenu
• it also adds a role="toolbar" which is not appropriate in this case.

Maybe I'm missing something but since BlockBreadcrumb is not focusable and can't be used with a keyboard, it should use any of that. If it's supposed to be a mouse-only feature, then it should be just a div without an ARIA role. Also, arrow navigation is pointless.

See also previous comment on the nested Cover Image PR #5452 (comment) where I'm suggesting to add the "Select parent block" button to the real block toolbar.

/Cc @jasmussen @jorgefilipecosta