feat: better plugin requirement checking

[justlevine]

What

Improves checks for plugin requirements, by reporting incompatible versions (WPGraphQL < v1.12.0 ) and incompatible plugins (WP GraphQL JWT Authentication), while allowing core functions to be overloaded.

Why

How

• feat: Improve requirement checks for WPGraphQL (required:v1.12.0) and WPGraphQL-JWT-Authentication(conflicted) plugins.
• dev: Allow core function overloading in wp-graphql-headless-login.php.

Testing Instructions

Additional Info

Checklist:

• [x] My code is tested to the best of my abilities.
• [x] My code follows the WordPress Coding Standards.
• [x] My code has proper inline documentation.
• [x] I have added unit tests to verify the code works as intended.
• [x] I included the relevant changes in CHANGELOG.md

[coveralls]

Coverage remained the same at 66.527% when pulling fbd901deff51cc82f22fb9b85217ba65092d68bd on justlevine:feat/better-plugin-requirement-checking into f05d04a1f815714cf20822cd7f9d8a9f29eac4c0 on AxeWP:develop.