Improve RouteText performance with pre-compilation of RegEx in certain cases

When using RegEx matches for the RouteText processor (and possibly other processors), the RegEx gets recompiled every time the processor works. The RegEx could be precompiled / cached under certain conditions, in order to improve the performance of the processor

See email from Mark Payne:

Re #2: The regular expression is compiled every time. This is done, though, because the Regex allows the Expression
Language to be used, so the Regex could actually be different for each FlowFile. That being said, it could certainly be
improved by either (a) pre-compiling in the case that no Expression Language is used and/or (b) cache up to say 10
Regex'es once they are compiled.