Composer/PHPCS: update to YoastCS 3.0.0

[jrfnl]

Context

• CI/QA update introducing YoastCS 3.0

Summary

This PR can be summarized in the following changelog entry:

• CI/QA update introducing YoastCS 3.0

Relevant technical choices:

Composer/PHPCS: update to YoastCS 3.0.0

YoastCS 3.0.0 has been released and is based on WordPressCS 3.0.0.

This commit makes the necessary updates for that:

• Composer: update the requirements.
• PHPCS ruleset:
  • Update a few sniff/property names for new names in WordPressCS 3.0.
  • Enforce strict PSR-4 for the tests.
  • Add configuration for the new WordPress.WP.Capabilities sniff.
  • Remove a few exclusions which are no longer needed.
  • Add a few selective exclusions for specific situations.
• GHA CS workflow: run the CS check on the latest PHP version. No need to run on PHP 7.4 any more as the deprecations previously encountered were all fixed.

Refs:

• https://github.com/Yoast/yoastcs/releases/tag/3.0.0
• https://github.com/WordPress/WordPress-Coding-Standards/releases/tag/3.0.0

GH Action/cs: use the threshold/branch report

... instead of a full scan.

As there are some YoastCS 3.0 issues which still need to be solved by the teams, this changes the CS workflow to use the threshold report instead of expecting a 100% clean code base.

Test instructions

Test instructions for the acceptance test before the PR gets merged

This PR can be acceptance tested by following these steps:

• If the build runs correctly and passes, we're good.

[coveralls]

Pull Request Test Coverage Report for Build 7229346582

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 50.203%

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Totals
Change from base Build 7229298252:	0.0%
Covered Lines:	1236
Relevant Lines:	2462

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💛 - Coveralls