ScriptUtils contains two calls to String#toCharArray for the sole
purpose to iterating over all chars in a String. Not only is this
unnecessary and can be replaced with String#charAt it also causes
additional allocator and heap pressure because String#toCharArray
rather than returning the backing array (which is gone in Java 9)
creates a copy.

This commit contains the following changes:

 - remove String#toCharArray from ScriptUtils and replace with
   String#charAt

Issue: SPR-15075