Backport: Elements - Merge element style and classname generation to single filter

[aaronrobertshaw]

Syncs the changes from WordPress/gutenberg#59535 and WordPress/gutenberg#59538.

These change update the elements block support filters such that the elements class name is only generated in a single location. This avoids conflicts between class names and makes the block support robust in the face of a block's data being filtered via other render_block_data filters.

To test:

Confirm WordPress/gutenberg#59462 is still resolved

1. Edit a post and add a paragraph
2. Create a link with the paragraph
3. Via the block inspector apply a link color to the paragraph
4. Save and view the frontend confirming the correct link color is shown
5. Confirm nested applications of the same element styles work correctly:

Create some nested blocks containing links

1. Apply a set of element styles to the parent block
2. Apply different styles to a child block
3. Apply the first set of element styles to a grand-child block
4. Confirm the correct display of element styles

Unit tests:

npm run test:php -- --filter Tests_Block_Supports_WpRenderElementsSupport
npm run test:php -- --filter Tests_Block_Supports_WpRenderElementsSupportStyles

Trac ticket: https://core.trac.wordpress.org/ticket/60681

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[aaronrobertshaw]

This PR is still only in a draft state as I have run out of time. Unfortunately, I'll be AFK until next week with limited bandwidth to push this across the line.

Anyone is welcome to pick this up, push to it, or create an alternate PR 🙏

[github-actions]

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[github-actions]

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[tellthemachines]

This is testing well for me! In order to reproduce the bug that this fixes, I dumped the filter that originally caused it in gutenberg into the layout.php file. I was then able to confirm that this change fixes the issue.

Just a couple minor corrections below, but otherwise looks good!

[aaronrobertshaw]

Thanks for the review @tellthemachines 👍

I've addressed the feedback 1789ecf & 8e60ca7.

[tellthemachines]

Thanks for the update! LGTM.

[tellthemachines]

Committed in r58074.

[mukeshpanchal27]

Remove end period.

[mukeshpanchal27]

Remove empty line.

[aaronrobertshaw]

@mukeshpanchal27 as these changes were already committed, I've created a follow-up PR to address the issues noted

• Fix coding standards issues in elements block supports #6488