Use a CSS parser to validate cosmetic rules

[ameshkov]

It will be useful if we are able to use a full-scale CSS parser for working with cosmetic rules.

Here's what it allows us to do:

1. Better cosmetic rules validation.
2. Change the way we pass cosmetic rules to the content script, part of the work can be done on the CoreLibs side (this point is a stretch, who knows what we can improve there).
3. It could be a step towards a CoreLibs version of AGTree: https://github.com/AdguardTeam/tsurlfilter/tree/master/packages/agtree

Discussion: https://github.com/AdguardTeam/AdguardForWindows/issues/1981