Update 6.1 CSS filter to match core

[andrewserong]

What?

Follow up to #43004 to backport a backport of the CSS filter from 6.1. This copies over the logic from https://github.com/WordPress/wordpress-develop/blob/2b4d385298504d412e9f0dea2e7019d53463c705/src/wp-includes/kses.php#L2504-L2512 in core, to make sure that Gutenberg + WP 6.0 has the same support for CSS functions as 6.1.

Why?

The previous version of this code wasn't current with core, and had edge cases that weren't allowed, as discussed in #43070 (comment).

How?

Copy + paste the lines from https://github.com/WordPress/wordpress-develop/blob/2b4d385298504d412e9f0dea2e7019d53463c705/src/wp-includes/kses.php#L2504-L2512 in core.

Testing Instructions

• Ensure that style engine tests still pass, e.g.

  gutenberg/phpunit/style-engine/class-wp-style-engine-css-declarations-test.php

  Line 157 in 388e5d2

  'background:var(--wp--preset--color--primary, 10px);font-size:clamp(36.00rem, calc(32.00rem + 10.00vw), 40.00rem);width:min(150vw, 100px);min-width:max(150vw, 100px);max-width:minmax(400px, 50%);padding:calc(80px * -1);background-image:url("https://wordpress.org");--wp--style--unstable-gallery-gap:12em;border-width:2000.75em;',

• Smoke test that layout styles on the site frontend are still working as expected
• Check that the copy+pasted lines are copy+pasted correctly 😀

[ramonjd]

Tested as part of #44961 😄 and following the tests in #43004

All unit tests pass

Thank you!!!