LibJS: Add Value::operator==()

This is needed for MarkedValueList::contains_slow() to work.

Userland/Libraries/LibJS/Runtime/Value.h

@@ -301,6 +301,8 @@ public:
 
     String typeof() const;
 
+    bool operator==(Value const&) const;
+
 private:
     Type m_type { Type::Empty };
 
@@ -383,6 +385,8 @@ bool same_value_zero(Value lhs, Value rhs);
 bool same_value_non_numeric(Value lhs, Value rhs);
 TriState abstract_relation(GlobalObject&, bool left_first, Value lhs, Value rhs);
 
+inline bool Value::operator==(Value const& value) const { return same_value(*this, value); }
+
 struct ValueTraits : public Traits<Value> {
     static unsigned hash(Value value)
     {