MULE-7277 Refactor for improved performance by using simple VariableResolverFactory implementations with less use of HashMaps
MULE-7277 Continue to use SafeReflective for now
Use methods rather than field access.
Fix code style
MULE-7277 Ensure variables are still immutable after changes.  Fix copy/paste error with dateTime function registration.
Merge pull request #386 from mulesoft/mel-performance

MULE-7277 Mel performance