Add test for :xpath and :nth-ancestor

[Mizzick]

Add tests for new pseudoclasses: :xpath and :nth-ancestor

Suuported platforms: Browser extension, Corelibs, Safari

More details:
AdguardTeam/ExtendedCss#86
AdguardTeam/ExtendedCss#96

[Alex-302]

:nth-ancestor

gorhill/uBlock@72bb700

New procedural cosmetic operator: `:upward(...)`

The purpose is to lookup an ancestor element.

When used with an integer argument, it is synonym of
`:nth-ancestor()`, which will be deprecated and which
will no longer be supported once no longer used in
mainstream filter lists.

Filter lists maintainers must only use `:upward(int)`
instead of `:nth-ancestor(int)` once the new operator
become available in all stable releases of uBO.

`:upward()` can also accept a CSS selector as argument,
in which case the nearest ancestor which matches the
CSS selector will be selected.