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;
+}
+
 }