Explicitly skip @requires module in PHPUnit Kernel and Browser tests

Follow-up to #2722731: Mark MissingDependentModuleUnitTest as incomplete →
Follow-up to #2721355: MissingDependentModuleUnitTest has the wrong namespace →

Problem/Motivation

This will I assume be expected functionality for feature parity coming from simpletest unit tests. This is related to 📌 Implement @requires and @dependencies within TestBase, mark tests as skipped Closed: outdated but implements the phpunit side only and fulfills the existing @todo in KernelTestBase.

Proposed resolution

Use @requires module modulename annotation at the class level and also at the test method level.

Disallow TestDiscovery from discarding tests that are annotated in this way.

Tests annotated this way will scan for the module on the filesystem and mark the test as skipped if the module is not present.

Remaining tasks

User interface changes

API changes

Does not change the API, but alters its behavior to make @require dependencies explicit.

Change record: https://www.drupal.org/node/2857979 →

Data model changes