* moved waiter from diagnostics.dll to features.dll where all interfaces are defined.

* simplified listener and waiter and moved those in product.

* cleaned up a bit

* fixed some comments

* forgot to add new AsyncListenerProvider in test export composition

* fixed dead lock found on unit tests

* remove all waiters left

* added dispatcher event processing in one more place

* added a way to enable waiter through env variable in test such as DDRIT

* added env var support so that It can be used without internalvisibleTo us.

* dont wait for all waiters but only onces each test used to wait.

* removed dependency to Roslyn.Services.Test.Utilities in integration test. that dll is not in probing path.

* fixed test failures

* fixed bug in integration tests

* move call to enable waiter before creating workspace so that workspace event queue get proper async listener

* expose concret type as well so that it can be directly used in test for waiter

* addressed PR feedbacks.

* rename mess up

* extra ) left out

* fixed build failure

fixed issue where same analyzer reference is installed in both vsix and nuget. deduplication in inproc analyzer manager wasn't present in OOP case. (#23772)

this doesn't address our workitem to merge those two. that work is a separate work item. this just follow what we currently do in proc.

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems?id=503862

previously, we set all work as done when we pass out last work from the queue without waiting that work to be done.

now, we raise works as done only when last item passed out are actually done.