AK: Enable direct comparsion of Optional<T> and T

This patch introduces a new operator== to compare an Optional to its
contained type directly. If the Optional does not contain a value, the
comparison will always return false.

This also adds a test case for the new behavior as well as comparison
between Optional objects themselves.

AK/Optional.h

@@ -100,6 +100,12 @@ public:
         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;
+    }
+
     ALWAYS_INLINE ~Optional()
     {
         clear();