Groovy Updater - Add NodeUpdateVisitorContext#isDryRun()

If there's an invocation on workflow APIs in groovy updater scripts, the "Dry run" option doesn't work properly because some workflow operations are all committed already.
I know it's kind of inevitable to have a separate dedicated jcr session used in the workflow operations.
So, as a workaround solution to support "Dry run", if a groovy script can know if it is in dry run mode through NodeUpdaterVisitorContext#isDryRun(), then an advanced groovy scripter may implement it not to surprise administrator executing the script somehow (e.g, skipping workflow operations on dry run mode).
I'm sure I have to make sure the script working fine locally without dry run option. That's something that I can endure with than being surprised afterward.