Incomplete ThreadPool API in NetStandard 2.1 comparing to NetCoreApp 3.0+

[dmitriyse]

The first framework that provides NetStandard 2.1 is NetCoreApp 3.0.
So NetStandard 2.1 have no limitations in adding API from .NetCoreApp 3.0

Despite some useful TheadPool methods are missing in the .Net Standard 2.1.
For example:

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

these methods are mandatory for the efficient implementation of the IValueTaskSource

Real life case:
The ManualResetValueTaskSourceCore<TResult> included into NetStandard 2.1, but if you try to copy-paste its sources and modernize for your needs
you will unable to do it being NetStandard 2.1 library, you need to upgrade to NetCoreApp 3.0.
If upgrade to NetCoreApp 3.0 is unacceptable then you need to have inefficient implementation - very disappointing problem where you don't expect it.

[benaadams]

/cc @stephentoub @terrajobst

[terrajobst]

Closing as not planned, as .NET Standard is considered complete.