Greg Wilkins

This could be 12.0 ... or perhaps best to be 12.1

@lorban thoughts?

> Seems like the `DefaultServlet` is now pretty much the same as the `ResourceServlet`? What are the actual differences? They are substantially similar, so the change is mostly in perception...

@joakime @lorban I added back the DefaultServletTest as it was, then added a bunch of parameterized tests for ResourceServletTest

@lorban slight javadoc change, so please review. @janbartel nudge.

I think the CI failures are flakes (we gotta get on top of that!)

@sbordet This PR is now also trying to undo the changes introduced in #11737 that meant we no longer compiled the code used in documentation. I think I've got it...

@joakime can you take a stab at writing a policy of where properties should be defined as currently we have a mix and it is not as simple as reverting...

The current status is that I have: + added the API to Callback + Done a basic implementation in Callback.Completing that substantially matches the API of IteratingCallback + added a...

@lorban @sbordet I have reimplemented ICB now and also written some more extensive tests so that I call abort in every state for every action and result. Coverage is pretty...