Remove several uses of VoidTaskResult (dotnet/coreclr#22238)

Remove several uses of VoidTaskResult  (dotnet/coreclr#22238)

* Remove defunct netstandard code from ValueTask

* Remove several uses of VoidTaskResult

Currently TrySetResult/Canceled/Exception live on `Task<T>`.  There's no reason `TrySetCanceled` and `TrySetException` need to live there, as they only access state from the base `Task`, and so can be moved down.  `TrySetResult` needs the `TResult`, however in a variety of cases `Task<T>` is used with a `VoidTaskResult`, and for such cases we can just have a parameterless `TrySetResult()` on the base class as well, which can be used any time there is no `TResult` or when `default(TResult)` is the desired result.  This lets us switch several cases where we were using `Task<VoidTaskResult>` to just be `Task`, which saves 8 bytes on the task instance on 64-bit.  It also avoids an Interlocked.Exchange as part of the TrySetResult call.

This primarily affects Task.Delay and the non-generic variants of Task.WhenAll, ValueTask.AsTask(), Task.FromCanceled, and Task.FromException.

Commit migrated from https://github.com/dotnet/coreclr/commit/5d5d680e64769f4807d2e114b74e1304a58822d5