Add key color roles, rename surfaces, adjust spec.

Done per chat and commentary on ag/21127519.

- Key colors are a new concept. A key color for a palette is found by
taking the palette's hue and chroma, and searching for the first tone
from T50 that reaches that chroma. Colors made using relativeLstar in
XML will now reach spec.
- Surface names changed after the code landed in the internal source
repo. This CL updates their names.
- Monet Gallery matches Android 2021's output. libmonet Java did not
match. Double-checked that Monet Gallery matched Android,
updated variant specs to match.

Bug: 266731167
Test: atest com.android.systemui.monet, all 389 pass.
Change-Id: I09a8ec9bd8883d124804db31369c595a6aca6a1b