Allow setting role attributes on core blocks

[carolinan]

What problem does this address?

Adding a role attribute, (for example role="button") to a core block causes a block validation error.
Allowing the role attribute would increase the flexibility for theme and plugin authors. It would compliment and not be as limited as the HTML element selection option that is in the Advanced panel for supported blocks.

To add a role attribute right now you would need to filter the block (or even create a custom block).

What is your proposed solution?

Similar to the aria label added in #41744, the role should be a block support but not have a UI, because it is an advanced feature.

[gziolo]

It sounds like a very good idea that is aligned with how other advanced HTML attributes are handled.