Compare pointers first in CSSCustomPropertyValue::equals()

https://bugs.webkit.org/show_bug.cgi?id=261057
rdar://114854431

Reviewed by Chris Dumez.

When CSSCustomPropertyValue holds a variant type that is a pointer, do pointer comparison first
before comparing values. This avoids calls to the expensive `CSSVariableData::operator==`, which
gives a measurable perf boost on some Speedometer 3 subtests with lots of custom properties.

* Source/WebCore/css/CSSCustomPropertyValue.cpp:
(WebCore::CSSCustomPropertyValue::equals const):

Canonical link: https://commits.webkit.org/267578@main

Source/WebCore/css/CSSCustomPropertyValue.cpp

@@ -56,11 +56,13 @@ bool CSSCustomPropertyValue::equals(const CSSCustomPropertyValue& other) const
     return WTF::switchOn(m_value, [&](const std::monostate&) {
         return true;
     }, [&](const Ref<CSSVariableReferenceValue>& value) {
-        return value.get() == std::get<Ref<CSSVariableReferenceValue>>(other.m_value).get();
+        auto& otherValue = std::get<Ref<CSSVariableReferenceValue>>(other.m_value);
+        return value.ptr() == otherValue.ptr() || value.get() == otherValue.get();
     }, [&](const CSSValueID& value) {
         return value == std::get<CSSValueID>(other.m_value);
     }, [&](const Ref<CSSVariableData>& value) {
-        return value.get() == std::get<Ref<CSSVariableData>>(other.m_value).get();
+        auto& otherValue = std::get<Ref<CSSVariableData>>(other.m_value);
+        return value.ptr() == otherValue.ptr() || value.get() == otherValue.get();
     }, [&](const SyntaxValue& value) {
         return value == std::get<SyntaxValue>(other.m_value);
     }, [&](const SyntaxValueList& value) {