Add new brightness aliases to keycodes_basic.md

[fauxpark]

Description

Just a slight tweak to the changes in #4836:

• Added the new aliases to keycodes_basic.md as well
• Aligned the keycode tables again
• Removed the references to the new aliases in KC_BRIU/D - it makes them seem like they don't work on macOS. I'm pretty sure they work across the board.

And removed some extra newlines in keycodes.md.

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

None.

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document. (https://docs.qmk.fm/#/contributing)
• 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).

[drashna]

Thanks!