Spring Reduce overhead of char[] creation

There are more locations which could benefit from not using a toCharArray on a String, but rather use the charAt method from the String itself. This to prevent an additional copy of the char[] being created.

Comment From: mdeinum

Additional note, while inspecting the AspectJAdviceParameterNameDiscoverer I noticed that it might be beneficial to extract the isVariableName method from the AbstractAspectJAdvice to a helper/utility class and use that from both classes. They share the same logic to determine if something is a variable name.