Elements: Add additional unit tests for elements block support

[aaronrobertshaw]

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

​https://github.com/WordPress/gutenberg/pull/55113

These changes add further unit tests for the element block support to better cover classname application and style generation.

This is a backport PR that includes the following PHP Gutenberg changes:

​https://github.com/WordPress/gutenberg/pull/55113

It provides additional unit tests for the elements block support and its associated classname and style generation.

Trac ticket: https://core.trac.wordpress.org/ticket/59555

[flixos90]

Per the guidance that exclusively performance related fixes shouldn't be labelled as enhancements, I'm changing this to a bug as it supports #59544.

Also, this ticket specifically is a tests only change, so it won't have any impact on the actual 6.4 release anyway.

Appreciate all the feedback @costdev & @felixarntz 👍

I believe I've addressed everything now. Let me know if I missed anything

Committed in https://core.trac.wordpress.org/changeset/56806 - which for some reason doesn't show up yet, but proof it was committed can be found here: ​https://github.com/WordPress/wordpress-develop/commit/4d5859bececc8b451ca95108d942f2a870bdf806 😆

[flixos90]

Fixed by [56806], which for some reason hasn't shown up here yet 🤔