[Keychron K4 V2 White] add initial support

[reyemxela]

Description

Initial support for Keychron K4 V2 White backlight.

I'm resubmitting this as a new PR because my original one was from a year+ ago and relied on a ton of 260 hacks at the time. Since then, there's been a lot of improvements on the 260 front, and it's working pretty well so far.

A few things that still need work:

• The backlight works with the new LED_MATRIX, but I don't seem to be getting any animations. Not sure if I need to be adding any more/different options to make those work now? I've tried a few things.
• Right now, the folder structure is only set up for the K4 White v2. If a v1 needs to be added, it probably needs a restructure to move some shared configs out to the main "white" parent folder.

Types of Changes

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

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.
• [ ] My change requires a change to the documentation.
• [ ] 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).

[github-actions[bot]]

Thank you for your contribution! This pull request has been automatically marked as stale because it has not had activity in the last 45 days. It will be closed in 30 days if no further activity occurs. Please feel free to give a status update now, or re-open when it's ready. For maintainers: Please label with bug, awaiting review, breaking_change, in progress, or on hold to prevent the issue from being re-flagged.

[github-actions[bot]]

Thank you for your contribution! This pull request has been automatically closed because it has not had activity in the last 30 days. Please feel free to give a status update now, ping for review, or re-open when it's ready. // [stale-action-closed]