Block delimiter: update class to be closer to original codebase

[jeherve]

Proposed changes:

Since the class does not rely on WordPress, we can afford to be more permissive, and not necessarily stick to WordPress coding standards.

This reverts some of the changes made in #43648.

It also updates PHPCS and Phan configuration to allow for errors.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

• p7H4VZ-5l1-p2#comment-12802
• 184026-ghe-Automattic/wpcom#pullrequestreview-349166

Does this pull request change what data or activity we track or use?

• No

Testing instructions:

This should not impact functionality. Tests should continue to pass. There should be no PHPCS or Phan errors.

[github-actions]

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[jp-launch-control]

Code Coverage Summary

Coverage changed in 1 file.

File	Coverage	Δ%	Δ Uncovered
projects/packages/block-delimiter/src/class-block-delimiter.php	208/275 (75.64%)	-13.30%	39 💔

Full summary · PHP report

_{Coverage check overridden by I don't care about code coverage for this PR Use this label to ignore the check for insufficient code coveage. .}