!str #15236 new transformer

This is far from finished, but I need to discuss.

The end goal of this is to provide a powerful, efficient, low level API for custom transformation operations. It is supposed to replace `Transformer`.

So far this is only using the API of the `impl.fusing.Op` (and subsclasses). These will be made more user friendly where needed. We can also consider providing higher level API that is more convenient for certain type of operations.

As first step I'm replacing all existing `Transformer` usage.

I'm currently stuck in `HttpEntity` and we must discuss how to go forward there. @jrudolph @sirthias should be part of that discussion.
@jrudolph I have to admit that I still don't understand all the details here, but if zip bomb is the main problem then the interpreter approach *might* help, but I might misunderstood what you need. But to give an example, if you have three ops, inputBytes -> unzip -> failIfTooManyBytes -> outputBytes, then the interpreter executes everything just as it was a stream, i.e. it does not construct immediate materialized full results but pulls things out as needed in a bounded fashion. So if unzip is implemented reasonably, so that chunks can be pulled out from it (and itself pulls out bytes from inputBytes), then the failIfTooManyBytes will terminate the whole stream before outputBytes grows too large. So even if this is synchronous it is bounded (of course the output bytes are not, but that is because it is a Strict element which materializes bytes fully -- if that is not desired then outputBytes should not be used, but this chain of ops should be directly plugged to their end consumer).

Maybe I am completely off the tracks here, so sorry if I misunderstood something, but I really want the new Ops infrastructure to work for everyone and tried to use many ideas from you and @sirthias in the implementation to have something reasonably fast and efficient that everyone can use either directly or building his own abstraction on top of it. So if there is something that is missing I want to fix it.