This PR is a cherry-pick of #61205 to release/10.3.

Original PR Description

Submission Review Guidelines:

• I have followed the WooCommerce Contributing Guidelines and the WordPress Coding Standards.
• I have checked to ensure there aren't other open Pull Requests for the same update/change.
• I have reviewed my code for security best practices.
• Following the above guidelines will result in quick merges and clear and detailed feedback when appropriate.

Changes proposed in this Pull Request:

(For Bug Fixes) Bug introduced in PR #60223

Since #60223, We always load legacy single product assets when using the Classic Template block. This is our effort to improve the frontend performance of the single product page for block themes (by not loading legacy assets by default).

However, this poses an issue for users of the Classic Template block, as they can not opt out of legacy gallery assets anymore using remove_theme_support. To resolve this, this PR follows the @Aljullu brilliant suggestion to let us respect theme supports on block themes.

How to test the changes in this Pull Request:

Using the WooCommerce Testing Instructions Guide, include your detailed testing instructions:

1. Add this snippet to the test site:

remove_theme_support( 'wc-product-gallery-zoom' );
remove_theme_support( 'wc-product-gallery-lightbox' );
remove_theme_support( 'wc-product-gallery-slider' );

2. Ensure the single product template use Classic Template block.

<!-- wp:template-part {"slug":"header","tagName":"header"} /-->
<!-- wp:group {"tagName":"main","layout":{"inherit":true}} -->
<main class="wp-block-group"><!-- wp:woocommerce/legacy-template {"template":"single-product"} /--></main>
<!-- /wp:group -->
<!-- wp:template-part {"slug":"footer","tagName":"footer"} /-->

3. Visit a product on the frontend, confirm the legacy gallery assets isn't loaded.