Fix remote theme patterns not rendering on the front end

[Haruto-works333]

What?

Closes #64104

Adds gutenberg_register_remote_theme_patterns() which registers remote theme patterns (from the Pattern Directory)
on init, so they are available when rendering templates on the front end.

Why?

When a theme registers a remote pattern via theme.json and references it in a template file (e.g., <!-- wp:pattern {"slug":"clients-section"} /-->), the pattern displays in the Site Editor but not on the front end.

This happens because _register_remote_theme_patterns() is only called from the REST API endpoint
(WP_REST_Block_Patterns_Controller::get_items()). The Site Editor triggers this endpoint, but front-end rendering
does not — so remote patterns are never registered.

Additionally, the core function cannot simply be hooked to init because it uses rest_do_request() internally,
which enforces the edit_posts permission check — causing it to silently fail for anonymous visitors.

How?

The new gutenberg_register_remote_theme_patterns() function:

• Fetches patterns directly from the WordPress.org API via wp_remote_get(), bypassing the REST permission layer
• Shares the same transient cache (1-hour TTL) used by WP_REST_Pattern_Directory_Controller, avoiding duplicate HTTP
  requests
• Applies the same sanitization as the REST controller's prepare_item_for_response()
• Respects the should_load_remote_block_patterns filter

Testing Instructions

1. Activate the Twenty Twenty-Four theme
2. Set reading settings to "Your latest posts" (Settings → Reading)
3. Edit wp-content/themes/twentytwentyfour/templates/home.html and add:

   <!-- wp:pattern {"slug":"clients-section"} /-->
   

4. Visit the front end — the "Clients Section" pattern should be visible

Testing Instructions for Keyboard

This change affects server-side pattern registration only. No UI or keyboard interaction changes.

Screenshots or screencast

Before	After

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Co-authored-by: HosseinKarami <hosseinkarami@git.wordpress.org>
Co-authored-by: SirLouen <sirlouen@git.wordpress.org>
Co-authored-by: sntran <sntran@git.wordpress.org>
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[github-actions]

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[Haruto-works333]

Hi, I've linked my GitHub and WordPress.org accounts after opening this PR. If this PR looks good to merge, could someone add the props-bot label to refresh the contributor list? Thank you!