Capture MethodRequest in Context to derive Reactor checkpoint

[HaloFour]

Refactors aspect instrumentation so that the request implements a common interface MethodRequest which is added to the Context. The ReactorAsyncOperationEndStrategy can then extract the MethodRequest and use it to get the name of the span in order to create a Reactor checkpoint.

[iNikem]

@HaloFour do you intend to finish this PR? Or should we close it to cleanup out list of PRs?

[HaloFour]

@iNikem

I would like to continue this branch but if you'd prefer I can close this PR and resubmit once I clean it up. Same goes for #3751.

[iNikem]

If you plan to continue working on this, then no problem, let it live :)

[trask]

same for this one

hi @HaloFour! any objection to closing this (just trying to clean up the backlog a little), and you can re-open when you start working on it again? I think if I close it you won't be able to re-open it, but if you close it, I think you will be able to re-open yourself. And of course you can always ping on the closed PR and one of us will re-open it if that fails.

[trask]

Closing, but please ping back if you start working on it again and would like it to be re-opened!