PHPCS: Exclude PHPUnit tests from file and class name sniffs (for Core parity)

[hellofromtonya]

What?

Use Core's file and class name sniffs exclusions for the PHPUnit tests.

Why?

To reduce the effort of backporting tests to Core by increasing parity to WordPress Coding Standards.

Test Classes and files in Core require the following:

Test class names should reflect the filepath, with underscores replacing directory separators and TitleCase replacing camelCase. Thus, the class Tests_Comment_GetCommentClass(), which contains tests for the get_comment_class() function, is located in tests/comment/getCommentClass.php.

So a test file is named as: group/funcName.php or group/className.php.

Core's tests include the same exclusions in its phpcs.xml.dist file.

How?

Testing Instructions

Before applying the patch:

1. Rename the class-wp-webfonts-test.php file to wpWebfonts.php.
2. Rename its class from WP_Webfonts_Test to Tests_Webfonts_WpWebfonts.
3. In terminal, run the linter on this file: npm run lint:php phpunit/wpWebfonts.php.

Results: WordPress.Files.FileName.NotHyphenatedLowercase linting error.

After applying the patch:
Rerun step 3 above. Results: No linting errors.

[anton-vlasenko]

I've followed the testing instructions.
I confirm that the PR works (no linting errors after applying the patch).
LGTM!

[hellofromtonya]

@anton-vlasenko Thank you for testing and reviewing!