TextEditor: Improve speed of hash function for font settings

The size of the array is fixed so we can simply use the memory patter as
a hash value.

Change-Id: If86a58b111a07b2bd9cecc12a03d74b93a914159
Task-number: QTCREATORBUG-16419
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: David Schulz <david.schulz@theqtcompany.com>

src/libs/utils/sizedarray.h

@@ -108,6 +108,11 @@ public:
         return m_size == 0;
     }
 
+    void fillWithZero()
+    {
+        std::array<T, MaxSize>::fill(T(0));
+    }
+
 private:
     std::uint8_t m_size = 0;
 };