Jetty-12 Rewrite RuleProcessor

[gregw]

This extracts some goodness from the closed #8793.
This PR decouples the rewrite module from the WrapperProcessor class, which is being considered for significant refactoring or removal. Having a module specific version of that class allows better code readability and a more appropriate API that avoids duplication request instances.

[sbordet]

I like the process(Response, Callback) method.

All the rest I am not sure.
Not sure whether having 2 abstractions that represent the same thing (a request wrapper that is also a request processor) makes sense.
Definitely not sold about reusability that I would remove for now from this PR until we settle on a decision.

[gregw]

@sbordet I removed all the residual re-use code (that was unintentional included by refactor).

I don't mind having two abstractions for Request + Processor, as I believe they will diverge as we clean up the issues in the Handler tree.
If they don't then, it will be trivial to change the parent of Rule.Processor to the common one. For now, the separation will allow us to experiment with Handlers without constantly breaking/fixing rewrite.

[sbordet]

LGTM, just clean up Rule.Processor as per comments.