Add Bit-C PRO converter

[jaygreco]

Description

Add the nullbits Bit-C PRO RP2040 to the converters so that existing projects can be converted easily. Tested by converting a TIDBIT and crkbd and ensuring the resulting file flashed properly, booted with the Bit-C PRO flash, and worked as expected: no missing/swapped rows/columns, and underglow working.

Types of Changes

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

Issues Fixed or Closed by This PR

• N/A

Checklist

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

[jaygreco]

Pinout attached for reference.