Added SetThreadDescription to set the unmanaged thread name (#12593)

Added SetThreadDescription to set the unmanaged thread name (#12593)

* Added SetThreadDescription to set the unmanaged thread name as well when a managed thread name was set.
This will show up in future debuggers which know how to read that information or in ETW traces in the Thread Name column.

* use printf  instead of wprintf which exists on all platforms.

* Removed printf
Ensure that GetProceAddress is only called once to when the method is not present.
Potential perf hit should be negligible since setting a thread name can only happen once per managed thread.

* - Moved SetThreadName code to winfix.cpp as proposed
- Finalizer and threadpool threads get their name
- GCToEEInterface::CreateBackgroundThread is also named
- but regular GC threads have no name because when I included utilcode.h things did break apart.

* Fix for data race in g_pfnSetThreadDescription

* Fix string literals on unix builds.

* Fixed nits
Settled thread name on ".NET Core ThreadPool"