Reusable blocks: "Export as JSON" link improvements

[afercia]

Follow up to #9788

When there are saved reusable blocks, a new list is available in the edit.php page to list the posts of type wp_blocks:

This page needs to follow the core best practices to make controls and links as accessible as possible. Specifically, with regards to the "Export as JSON" link:

1
The aria-label needs to reference the post (reusable block) name, otherwise when in this page there will be several saved blocks, there will also be several "Export as JSON" links without any context; notice the reference to the post is already used for all similar action links in core. e.g.:

• Edit “Hello world!” in the classic editor
• Quick edit “Hello world!” inline
• Move “Hello world!” to the Trash
• etc.

In the same way, this new link should contain the reusable block name, e.g.:

• Export “My address" as JSON

2
For no reason, ever, new links with a href="#" attribute should be introduced in core. For a number of years, WordPress has been progressively removing this kind of "links", as they're not real links: the href attribute is just an incomplete URL fragment identifier, and the link doesn't trigger navigation. A button should be used instead.

Note: I've seen #10000