For PHP8+: Remove deprecated stylelint rule and rename PHPCS rule

[raikasdev]

• number-leading-zero rule was deprecated in Stylelint version 15.0.0 due to "pretty printing" features removed and focusing on linting itself. (Migrating to Prettier for SCSS linting?)
• WordPress.WhiteSpace.PrecisionAlignment has been replaced by Universal.WhiteSpace.PrecisionAlignment in 3.0.0 (changelog entry)

[height]

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[ronilaukkarinen]

@raikasdev PHPCS fails to error ERROR: Referenced sniff "PHPCSUtils" does not exist. Can't get it to work on master or develop either, had to get -b 2.2.0. Strange. But unit test should go through, can you try and test it again? 🤔

[raikasdev]

Ah, in 3.0.0 of the WordPress PHPCS rules PHPCSUtils was added as a dependency (might have been built-in before) and must be installed. I'll add them to the workflow, but they also need to be added to documentation (devpackages README also?)

3.0.0 is for PHP 8 support, so this PR isn't perhaps that critical right now, but as PHP 7.4 has reached end-of-life already and the WP team is trying to get PHP 8 full support released, probably good to have this ready.

"Dependencies on the following packages: PHPCSUtils, PHPCSExtra and the Composer PHPCS plugin."

[ronilaukkarinen]

Added separately without this PR.