LibJS: Enable storing Value and Handle<Value> in HashMaps

We have the right conversions to make this work, so let's make it
possible to have a `HashMap<JS::Handle<T>, V>` and look for a specific
T inside it without having to create a temporary handle.

This involves adding some operator== implementations, and some
specializations of AK::Traits.

Userland/Libraries/LibJS/Runtime/Value.h

@@ -619,6 +619,18 @@ public:
         return *this;
     }
 
+    template<typename O>
+    ALWAYS_INLINE bool operator==(Optional<O> const& other) const
+    {
+        return has_value() == other.has_value() && (!has_value() || value() == other.value());
+    }
+
+    template<typename O>
+    ALWAYS_INLINE bool operator==(O const& other) const
+    {
+        return has_value() && value() == other;
+    }
+
     void clear()
     {
         m_value = {};
@@ -688,4 +700,9 @@ struct Formatter<JS::Value> : Formatter<StringView> {
     }
 };
 
+template<>
+struct Traits<JS::Value> : GenericTraits<JS::Value> {
+    static unsigned hash(JS::Value value) { return Traits<u64>::hash(value.encoded()); }
+};
+
 }