Apply wpseo_sitemap_links filter to return value get_sitemap_links()

[SeanDKendle]

Context

• Give the ability to filter or add to the sitemap links list. This was necessary for our project to add custom routes to our sitemap that aren't generated from post objects.

Summary

This PR can be summarized in the following changelog entry:

• Apply wpseo_sitemap_links filter to return value get_sitemap_links() to give the ability to filter or add to the sitemap links list

Relevant technical choices:

Test instructions

Test instructions for the acceptance test before the PR gets merged

This PR can be acceptance tested by following these steps:

• Simply use add_filter() to filter the sitemap links in the theme's functions.php file, e.g.:

    //This will add /test to the end of all page routes to prove it works
    add_filter('wpseo_sitemap_links_page', function($links, $post_type, $posts) {
        if($post_type !== 'page')
            return $links;

        $new_links = [];

        for($i = 0; $i < count($links); $i++) {
            $links[$i]['loc'] = trailingslashit($links[$i]['loc']) . 'test';
            $new_links[] = $links[$i];
        }
        return $new_links;
    }, 10, 3);

• Then, navigate to /page-sitemap.xml to check that all links now have /test at the end.

Relevant test scenarios

• Changes should be tested with the browser console open
• Changes should be tested on different posts/pages/taxonomies/custom post types/custom taxonomies - this PR allows editing/filtering/removing any of the links returned from get_sitemap_links(), so it should apply universally to all routes. Our code, for example, uses a custom taxonomy products and our filter looks like this: add_filter('wpseo_sitemap_links_product', [$this, 'products_sitemap_filter'], 10, 3);
• Changes should be tested on different editors (Default Block/Gutenberg/Classic/Elementor/other)
• Changes should be tested on different browsers
• Changes should be tested on multisite

Test instructions for QA when the code is in the RC

• QA should use the same steps as above.

QA can test this PR by following these steps:

Impact check

This PR affects the following parts of the plugin, which may require extra testing:

• This PR should not affect anything unless using the filter above, in which case, the links will be filtered

Other environments

• This PR also affects Shopify. I have added a changelog entry starting with [shopify-seo], added test instructions for Shopify and attached the Shopify label to this PR.
• This PR also affects Yoast SEO for Google Docs. I have added a changelog entry starting with [yoast-doc-extension], added test instructions for Yoast SEO for Google Docs and attached the Google Docs Add-on label to this PR.

Documentation

• I have written documentation for this change. For example, comments in the Relevant technical choices, comments in the code, documentation on Confluence / shared Google Drive / Yoast developer portal, or other.

Quality assurance

• I have tested this code to the best of my abilities.
• During testing, I had activated all plugins that Yoast SEO provides integrations for.
• I have added unit tests to verify the code works as intended.
• If any part of the code is behind a feature flag, my test instructions also cover cases where the feature flag is switched off.
• I have written this PR in accordance with my team's definition of done.
• I have checked that the base branch is correctly set.
• I have run grunt build:images and commited the results, if my PR introduces new images or SVGs.

Innovation

• No innovation project is applicable for this PR.
• This PR falls under an innovation project. I have attached the innovation label.
• I have added my hours to the WBSO document.

Fixes #

[BillyHilly]

+100!
This would be very handy in more advanced ACF setups.