Fail if config.h-migrateable entities aren't in keyboard.json.

[tzarc]

Description

Now that the config.h ordering has been somewhat sorted (#23448, keyboard before generated info_config.h before keymap), this will ensure that if there are keyboard-level items in config.h cause failures during build, prompting migration.

Additionally, a large chunk of documentation will need to be migrated away from promoting the use of config.h before we could consider merging this.

This is raised early for visibility purposes and is not expected to be merged any time soon; almost all migrations will need to occur first, otherwise there will be hundreds of build failures.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).