Sharing: fix a11y issues in buttons' links

[monsieur-z]

Fixes #30474

Proposed changes:

This PR fixes the accessibility problems mentioned in the linked issue. In detail:

• It removes the title attribute from the a tag. A title is not the recommended way to specify an accessible name.
• Instead, the accessible name is specified by linking a text element with aria-labelledby. It's preferred over the aria-label attribute as the latter may not be picked up by automated translation services.
• It deprecates jetpack_sharing_display_title in favor of a new filter named jetpack_sharing_accessible_name to mitigate confusion.
• It removes the sharing-screen-reader-text class (and the associated CSS rules) which is no longer necessary since the accessible name is specified with aria-labelledby.
• It was suggested in the issue to add the aria-haspopup attribute. According to the MDN docs, this doesn't seem appropriate to this use case since activating the link opens a new window. The accessible name mentions a new window will be open.
• It formats the markup returned by get_link for better readibility.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

n/a

Does this pull request change what data or activity we track or use?

No.

Testing instructions:

Note: on this branch like on trunk, sharing buttons are rendered the same no matter the value of the Sharing_Source::button_style attribute.

• Spin up a Jetpack site with this branch
• Toggle on the Add sharing buttons to your posts and pages option in /wp-admin/admin.php?page=jetpack#sharing
• Create a new post
• Publish it (saving a draft is not sufficient)
• View the post
• Notice the sharing buttons below the post. Verify they work as expected.
• If you're able to use a screen reader, check it announces something like link, Click to share on Facebook (Opens in new window) when it reaches a sharing button
• Otherwise, verify the button markup is similar to:

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WoA dev site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin (Jetpack), and enable the fix/sharedaddy-button-a11y branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack fix/sharedaddy-button-a11y

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[github-actions]

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Code Coverage Summary

Coverage changed in 1 file.

File	Coverage	Δ%	Δ Uncovered
projects/plugins/jetpack/modules/sharedaddy/sharing-sources.php	106/988 (10.73%)	1.31%	-3 💚

Full summary · PHP report · JS report

[monsieur-z]

replace-next-version-tag.sh doesn't replace $$next-version$$ in this instance.

[manzoorwanijk]

It should be a single line to make work.

[jeherve]

Do we need to do the same for the Sharing Buttons block?

jetpack/projects/plugins/jetpack/extensions/blocks/sharing-button/class-sharing-source-block.php

Line 172 in d0f8e92

public function get_link( $post_id, $query = '', $id = false, $data_attributes = array() ) {