Insert block template skip link via HTML API, minify CSS, remove JS.

[rutviksavsani]

Move the block template skip link from client-side injection to server-side HTML processing using the HTML API, while keeping the existing accessibility behaviour and minifying the CSS.

What this changes

• Adds _block_template_skip_link_markup() to process the block template HTML:

  • Ensures the first <main> has an id (adds wp--skip-link--target if missing).
  • Inserts a single <a id="wp-skip-link" class="skip-link screen-reader-text"> before .wp-site-blocks.
  • Skips insertion when there is no <main> or when a skip link already exists.

• Updates get_the_block_template_html() to run the rendered template through the new helper.

• Refactors wp_enqueue_block_template_skip_link() to:

  • Remove the old JS-based DOM injection.
  • Minify the skip-link CSS as an inline style.

• Preserves backward compatibility gating via the_block_template_skip_link and block-templates theme support.

• Add tests for the new function as well.

Ticket

Trac ticket: https://core.trac.wordpress.org/ticket/64361

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Props rutviksavsani, westonruter.

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[westonruter]

Great to see this!

[westonruter]

We might want to consider inlining the logic instead of adding a new global function which is only used in one place.

[rutviksavsani]

@westonruter I initially considered inlining it but the for readability and testability, I went with a separate function and noticed in the codebase as well we follow the similar structure at many places.

If you feel we can still merge it into the main functions. I can do it as well.