style: Add simple parsing and matching support for :has

Parsing is behind a config value `layout.css.has-selectors.enabled`. This
change does not support p:has(> a) combinators, but will handle them
gracefully, just not matching on them.

Differential Revision: https://phabricator.services.mozilla.com/D149515

components/malloc_size_of/lib.rs

@@ -695,7 +695,9 @@ where
             Component::Slotted(ref selector) | Component::Host(Some(ref selector)) => {
                 selector.size_of(ops)
             },
-            Component::Is(ref list) | Component::Where(ref list) => list.size_of(ops),
+            Component::Is(ref list) |
+            Component::Where(ref list) |
+            Component::Has(ref list) => list.size_of(ops),
             Component::PseudoElement(ref pseudo) => (*pseudo).size_of(ops),
             Component::Combinator(..) |
             Component::ExplicitAnyNamespace |