Update YMDK YMD75 rev3 to match rev4

[sodevel]

Description

This PR updates the rev3 to match the improvements i made for the rev4 in #26204. Additionally, it enables NKRO (i don't know why it was disabled), Backlight Breathing (so the setting in VIA does finally do something) and sets Bootmagic to really use the ESC key.

I removed the GBP £ Macro from the default keymap, both revisions now use almost the same keymap, rev3 has some extra keycodes to control the backlight.

I own PCBs of both revisions and can confirm the changes do work for me.

Types of Changes

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

Issues Fixed or Closed by This PR

• None

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).