RFC: Add aliases for common UI cases

[mvllow]

This one needs some cooking, but here's a non-exhaustive list that is bound to change or even be scrapped altogether:

Alias	Variable
$border	$muted/20
$tonal.love.bg	$love/10
$tonal.love.border	$love/20
$tonal.love.fg	$love
$item.fg	$subtle
$item.hover.bg	$muted/10
$item.hover.fg	$text

I think we could get a little wild if we're not careful. This would need to be done thoughtfully as we don't want to create an entire design system. We still want to encourage people to use Rosé Pine how they want, not how we want. The tonal aliases fit this philosophy where the border may not.