Digitizer feature improvements

[fauxpark]

Description

• Improved documentation, added API reference
• Added support for barrel switch alongside tip switch
• Replaced enum digitizer_status with simple dirty flag in digitizer_t
• Removed digitizer_task() as it now doesn't do anything - reports are sent as needed
• Added header include to quantum.h so user code does not need to
• Adjusted USB desriptors and fixed V-USB to match
• Updated onekey keymap to showcase changes

Types of Changes

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

Issues Fixed or Closed by This PR

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).