AK: Make HashMap::get(Key) return an Optional<Value>.

This allows HashMap::get() to be used for value types that cannot be default
constructed (e.g NonnullOwnPtr.)

AK/Optional.h

@@ -103,7 +103,9 @@ public:
         return fallback;
     }
 
+    operator bool() const { return has_value(); }
+
 private:
-    char m_storage[sizeof(T)] __attribute__((aligned(sizeof(T))));
+    char m_storage[sizeof(T)];
     bool m_has_value { false };
 };