LPS-39703 Add fast paths for ascii code only String's toLowerCase() and toUpperCase()

Brian, after you merge this change, there are 2 things need to be done.
1) Can you have someone to globally search for ".toLowerCase()" and ".toUpperCase()" on all *.java, *.jsp and *.jspf to apply it?
2) Have Hugo to add a source formatter rule to stop people from using String.toLowerCase() and String.toUpperCase() in the future.