Support SQLCLR in .NET core

[mdaigle]

Is your feature request related to a problem? Please describe.

SQLCLR is only supported when using .NET Framework.

Describe the solution you'd like

Extend support to .NET core.

Additional context

See: #3234

[Wraith2]

This has previously been discussed as part of merging differences in the two codebases. IMO it is not possible to use .net core inside sql server, as i said here #3535 (comment)

Netcore and now NET is not and will never be a supported host in sql server because much of the work done to improve netcore over netfx was removal of things that SQLCLR needed. Things like being able to terminate at any arbitrary point in execution without corrupting the runtime are simply not possible and were a constant source of bugs. ThreadAbortException, CER and related work were part of this featureset and have been removed.