LibWeb: Skip pending :has() invalidations if there are no :has()

`invalidate_style()` already tries to avoid scheduling invalidation for
`:has()` by checking result of `may_have_has_selectors()`, but it might
still result in unnecessary work because `may_have_has_selectors()`
does not force building of rules cache. This change adds
`have_has_selectors()` that forces building of rules cache and is
invoked in `update_style()` to double-check whether we actually need to
process scheduled `:has()` invalidations.

This allows to skip ~100000 ancestor traversals on this WPT test:
https://wpt.live/html/select/options-length-too-large.html

Libraries/LibWeb/CSS/StyleComputer.cpp

@@ -3172,4 +3172,10 @@ bool StyleComputer::may_have_has_selectors() const
     return m_selector_insights->has_has_selectors;
 }
 
+bool StyleComputer::have_has_selectors() const
+{
+    build_rule_cache_if_needed();
+    return m_selector_insights->has_has_selectors;
+}
+
 }

Libraries/LibWeb/CSS/StyleComputer.h

@@ -177,6 +177,7 @@ class StyleComputer {
     void collect_animation_into(DOM::Element&, Optional<CSS::Selector::PseudoElement::Type>, GC::Ref<Animations::KeyframeEffect> animation, ComputedProperties&, AnimationRefresh = AnimationRefresh::No) const;
 
     [[nodiscard]] bool may_have_has_selectors() const;
+    [[nodiscard]] bool have_has_selectors() const;
 
     size_t number_of_css_font_faces_with_loading_in_progress() const;
 

Libraries/LibWeb/DOM/Document.cpp

@@ -1665,12 +1665,22 @@ void Document::invalidate_style_of_elements_affected_by_has()
         return;
     }
 
+    ScopeGuard clear_pending_nodes_guard = [&] {
+        m_pending_nodes_for_style_invalidation_due_to_presence_of_has.clear();
+    };
+
+    // It's ok to call have_has_selectors() instead of may_have_has_selectors() here and force
+    // rule cache build, because it's going to be build soon anyway, since we could get here
+    // only from update_style().
+    if (!style_computer().have_has_selectors()) {
+        return;
+    }
+
     for (auto const& node : m_pending_nodes_for_style_invalidation_due_to_presence_of_has) {
         if (node.is_null())
             continue;
         node->invalidate_ancestors_affected_by_has_in_subject_position();
     }
-    m_pending_nodes_for_style_invalidation_due_to_presence_of_has.clear();
 
     // Take care of elements that affected by :has() in non-subject position, i.e., ".a:has(.b) > .c".
     // Elements affected by :has() in subject position, i.e., ".a:has(.b)", are handled by