Make templates fallback methods template-agnostic

[Aljullu]

In #44778 we are working on a refactor that will simplify how templates that fall back to another template work (aka Products by Category/Tag/Attribute falling back to the Product Catalog template when they haven't been customized).

Unfortunately, that PR has some upstream blockers, so it's unlikely that we will be able to merge it anytime soon. So I'm creating this PR to port some improvements from that PR into trunk.

Specifically, this PR:

• Gets rid of the template_is_eligible_for_product_archive_fallback() method, as knowing if a template is elligible for fallback is as easy as checking if $template->template_fallback exists.
• Refactors all templates_is_eligible_for_product_archive_fallback... methods to be template-agnostic, that means removing product_archive from the method name and checking for the template_fallback property, instead of only checking for the Product Catalog slug.

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:

Part of #42251.

How to test the changes in this Pull Request:

This PR doesn't change the behavior of how WooCommerce templates currently work in the Site Editor. Hopefully any issues would be evident (ie: a PHP fatal) or would be caught by e2e tests, but in any case, in order to do some smoke testing:

1. Go to Appearance > Editor and make some edits to the Product Catalog and Products by Category template.
2. Go to the Shop page in the frontend (/shop) and verify the edits you did in the Product Catalog template are visible.
3. Go to a category page in the frontend (ie: /product-category/clothing) and verify the edits you did in the Products by Category template are visible.
4. Go to a tag page in the frontend (ie: /product-tag/recommended, note: you might need to create the tag first from Products > Tags) and verify the edits you did in the Product Catalog template are visible.
5. Revert the editions.
6. Visit the frontend pages again and verify there are no edits.

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• Patch
• Minor
• Major

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• Fix - Fixes an existing bug
• Add - Adds functionality
• Update - Update existing functionality
• Dev - Development related task
• Tweak - A minor adjustment to the codebase
• Performance - Address performance issues
• Enhancement - Improvement to existing functionality

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