Site Title: Extract Heading Level Dropdown from Heading block, re-use

[ockham]

We have a component at packages/block-library/src/heading/heading-level-dropdown.js which seems to be very similar to the one used by Site Title. Probably we should extract the component from the Heading block and reuse it here.

(Per @david-szabo97 in #24758.)

[ZebulanStanphill]

It's worth noting the current a11y issues with the Heading block's implementation that should probably be resolved before using it for other blocks.

[Addison-Stavlo]

From what I am gathering from that issue:

While the current implementation works , this issue is more about what users would expect

This seems more of a design concern than an accessibility blocker. We should be able to move forward with extracting this component for re-use, as making improvements on it in the future would then improve the flow everywhere it is used.

[ZebulanStanphill]

@Addison-Stavlo That's a good point, and I would not be opposed to a PR to go ahead and merge the two implementations. However, there is one more thing I should point out:

The Heading block's level dropdown uses icons for its visible option labels. Normally, this would be less than ideal, but the icons in this case are almost just text. (H1, H2, etc.) In the case of the Site Title block, displaying the text as a Paragraph is an option, which as an icon would have to be represented either using the icon we already use for the Paragraph block, or else a "P". I don't think this is ideal, especially for users that aren't English-speaking.

I'm starting to wonder if perhaps the Site Title block's tag dropdown should be ported to the Heading block, rather than the other way around. The Site Title block's dropdown is clearly the better-implemented of the two.

[skorasaurus]

This can be closed thanks to the work done in #46003