Elements: Fix application of element class name when attributes are filtered

[aaronrobertshaw]

This ticket tracks the backporting of PHP files for the following Gutenberg changes:

• ​https://github.com/WordPress/gutenberg/pull/59535

These changes fix a bug where if the block data was filtered via render_block_data the elements CSS class wouldn't be consistently applied breaking the feature.

The initial solution that was merged in Gutenberg via ​https://github.com/WordPress/gutenberg/pull/59533 caused a conflict in CSS classes that ​https://github.com/WordPress/gutenberg/pull/59535 addresses.

Syncs the changes from ​https://github.com/WordPress/gutenberg/pull/59535.

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 ​https://github.com/WordPress/gutenberg/issues/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

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 🙏

[jorbin]

Based on ​https://github.com/WordPress/gutenberg/pull/59535#issuecomment-1992881732 I am moving this to 6.6

Thanks for the review @tellthemachines 👍

I've addressed the feedback ​https://github.com/WordPress/wordpress-develop/pull/6214/commits/1789ecf5fd659aa1da57c165cfc0086720c6e185 & ​https://github.com/WordPress/wordpress-develop/pull/6214/commits/8e60ca74fd4098e484488757b154e8e877610615.

[isabel_brison]

In 58074:

Editor: Merge element style and classname generation to single filter.

Fixes element classnames not being output when block attributes are filtered with render_block_data.

Props aaronrobertshaw, isabel_brison, jorbin.
Fixes #60681.

Committed in r58074.

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

• ​https://github.com/WordPress/wordpress-develop/pull/6488

[isabel_brison]

In 58090:

Editor: Fix coding standards and move deprecated function to correct file.

Follow-up to [58074], formats docblocks correctly and moves wp_render_elements_support to the deprecated file.

Props aaronrobertshaw, isabel_brison, mukesh27, spacedmonkey.
See #60681.