Block API: Render alias block with canonical block class name

[tjcafferkey]

Trac ticket:

Consider the following markup:

<!-- wp:social-links -->
<ul class="wp-block-social-links">
	<!-- wp:social-link {"url":"Tumblr.com","service":"tumblr"} /-->
	<!-- wp:core/social-link/wordpress {"url":"wordpress.com","service":"wordpress"} /-->
</ul>
<!-- /wp:social-links -->

The second social link has an alias core/social-link/wordpress which we need to render correctly on the frontend with the correct CSS class names.

All WP_Block_Type's are registered under their canonical form, meaning aliases are not in the registry. So when we are rendering an alias block type we need to know what the alias is so we can generate the appropriate class names for it, for the above mark up this would be: wp-social-link wp-social-link-wordpress wp-block-social-link.

This PR uses a new utility function to check if the block name we are generating a class name for is a variation (e.g. has an alias) or not and if so we generate an additional CSS class for the canonical block name.

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[tjcafferkey]

Maybe instead of amending the WP_Block_Type_Registry->get_registered() method to derive the canonical block name, we should do it here? I'm not sure.