API Proposal: Add generic UnsafeQueueUserWorkItem<TState> overload

[davidfowl]

In .NET Core 2.1 we added a generic overload of QueueUserWorkItem that can avoid boxing the state parameter https://github.com/dotnet/corefx/issues/27464#issue-300109510. We should add the same overload for UnsafeQueueUserWorkItem. I'd like to use this in pipelines to offer a PipeScheduler that avoids capturing the ExecutionContext.

public static bool UnsafeQueueUserWorkItem<TState>(Action<TState> callBack, TState state, bool preferLocal)

cc @stephentoub

[benaadams]

Could this be 3.0?

[davidfowl]

It must 😬. There’s at least one other thing that want me to use this in 3.0

[benaadams]

Add the 3.0 milestone? They get preference in api reviews

[terrajobst]

Given that we already approved the Unsafe* pattern here and that we did this overload for the non-unsafe ones, there is no reason not to approve this :-)