Fix phpstan: Use stubs, instead of ignoring

[carstingaxion]

After #931 was merged, I realized, that GatherPress could still benefit from type checking for the ignored, not-loaded constants.

Description of the Change

Instead of ignoring, I created stubs, that provide at least the type of data.

Closes #

How to test the Change

composer test:phpstan

Changelog Entry

Fixed - phpstan: Use stubs, instead of ignoring

Credits

Props @carstingaxion

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests pass.

[what-the-diff]

PR Summary

• Enhancement in Code Quality Configuration Files

  • An ongoing process to improve our software's code quality involved the refinement of our phpstan.neon.dist file. This file enables us to check our code's reliability systematically. We've eradicated unnecessary commented-out paths, contributing to a more streamlined, readable configuration.

• Removal of Ignoring Unknown Constants

  • This update also eradicates some ignore error patterns from the phpstan.neon.dist file. These were earlier employed to overlook undefined constants, like GATHERPRESS_CACHE_GROUP, GATHERPRESS_CORE_FILE, etc. that came across in the code quality checks. This clean-up attempt results in more comprehensive and accurate code quality checks.

• Explicit Declaration of Constant Definitions

  • We've revisited phpstan.stubs file, enabling us to declare the constants (GATHERPRESS_CACHE_GROUP, GATHERPRESS_CORE_FILE, GATHERPRESS_CORE_PATH, GATHERPRESS_CORE_URL, GATHERPRESS_REST_NAMESPACE, GATHERPRESS_REQUIRES_PHP) explicitly with default values. It fosters improved code understanding, readability, and predictability.