AK: Rename ValueRestorer => ScopedValueRollback.

Qt had a pretty good name for this concept, so let's steal it. :^)

AK/ScopedValueRollback.h

@@ -0,0 +1,26 @@
+#pragma once
+
+namespace AK {
+
+template<typename T>
+class ScopedValueRollback {
+public:
+    ScopedValueRollback(T& variable)
+        : m_variable(variable)
+        , m_saved_value(variable)
+    {
+    }
+
+    ~ScopedValueRollback()
+    {
+        m_variable = m_saved_value;
+    }
+
+private:
+    T& m_variable;
+    T m_saved_value;
+};
+
+}
+
+using AK::ScopedValueRollback;