Add helper function to (un)escape illegal JCR characters

I have files with names that contain illegal JCR characters (e.g. square brackets).
Trying to insert them into ModeShape as-is doesn't work of course.
What about providing an helper function to (un)escape those illegal characters?

JackRabbit provides such a function: org.apache.jackrabbit.util.Text.escapeIllegalJcrChars()

According to MODE-1930, such a (non-generic) function has been developed for the DDL sequencer. So I think this should migrate from the DDL sequencer to the common framework.

Ed: ModeShape has a utility in the 'modeshape-common' library. We should either suggest people use that or provide something in our official API within the org.modeshape.jcr.api package.