feat(material/theming): Add palette values to system variables

[amysorto]

Feature Description

Prior to the theme mixin you could access palette tone colors from the theme object. It would be useful to add this as system variables for parity. Apps that use the theme mixin don't have a theme object anymore and may still want to access those colors.

Use Case

No response

[MikaStark]

IMO, it could be nice to also have typography variables such like (not just colors) :

--mat-sys-plain-family: Roboto;
--mat-sys-brand-family: Roboto;
--mat-sys-bold-weight: 700;
--mat-sys-medium-weight: 500;
--mat-sys-regular-weight: 400;

[msrumon]

This should be among the top-priority todos