Add public getDelegate method to all visitor classes.

Currently, only the RecordComponentVisitor offers a public method for reading the underlying visitor. Sometimes, it is however desirable to communicate with a visitor that lies beneath another visitor also for the other visitor implementations. Could an equivalent getter be added for the other visitors, too?

Also, would you consider to make the delegate field for the record component visitor protected as with the other visitors? This can be handy when a subclass of a visitor wants to change its delegate after visiting some properties, for example after all attributes were passed. Ideally, ASM would be consistent here.