Nav Unification: update Calypso color schemes for nav-unification

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Heads up; in addition to porting them to wp-admin, all of these schemes need changes in calypso, too. If you turn on one of these schemes in calypso, then turn on the nav-unification flag, you still see the old wp-admin colorscheme in calypso.

Changes Needed
The scope of the scheme's current variable settings needs to be expanded to include .is-nav-unification.
Some additional color variables that only exist in calypso nav unification need to be set. These are submenu colors which exist in wp-admin and nav unification, but not regular calypso.

See #47040 (comment)

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Solved via the following list of PRs

update Classic Blue color scheme to be compatible with Nav Unification #47709
update Classic Bright color scheme to be compatible with Nav Unification #47728
update Classic Dark color scheme to be compatible with Nav Unification #47730
update Contrast color scheme to be compatible with Nav Unification #47746
update Nightfall color scheme to be compatible with Nav Unification #47751
update Powder Snow color scheme to be compatible with Nav Unification #47752
update Sunset color scheme to be compatible with Nav Unification #47786