Make a layer token on css variables

[a1eksandrk]

Make a layer token on css variables. There are components that use z-index, it would be nice to standardize the use of this property to avoid problems with overlapping components (such a problem exists when using Drawer next to Table which has a sticky column). What do you think about this?

For example:
--utility-layer: 10;.
--drawer-layer: 100;
--modal-layer: 1000;

[korvin89]

@a1eksandrk Hey! We already have this mechanism.

@DarkGenius Hey! What do you think about using layer manager in Drawer?

[amje]

Issue about Drawer: gravity-ui/navigation#208