RGBLight: Improve RGB Test animation

[fauxpark]

Description

Just for fun. The animation now cycles through all combinations of RGB, instead of just each channel individually, and also respects UG_VALU/UG_VALD rather than simply using RGBLIGHT_LIMIT_VAL.

Binary	Colour
001	Red
010	Green
011	Yellow (Red+Green)
100	Blue
101	Pink (Red+Blue)
110	Cyan (Blue+Green)
111	White (Red+Green+Blue)
000	Off

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

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).