Support for :scope and :has selectors

[kraih]

These two CSS 4 selectors are supported by Mojo::DOM and still missing in @mojojs/dom.

Pattern	Represents
E:scope	an E element being a designated reference element
E:has(rs1, rs2, …)	an E element, if either of the relative selectors rs1 or rs2, when evaluated with E as the :scope elements, match an element

Scope handling already partially exists in the code, but is not used for anything yet.

[kraih]

Commit that added :scope. mojolicious/mojo@bd2602d

[kraih]

Commit that added :has. mojolicious/mojo@5084309