Move the implementation of Win32Exception into System.Private.CoreLib

[jkoritzinsky]

Required for #57610

[ghost]

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[stephentoub]

Should we consider introducing a exception type named better? We could move all the logic from Win32Exception into it and make Win32Exception derive from it. It's just such unfortunate naming. We've accepted that for existing code, but it seems nice to avoid using it in more places.

[jkotas]

The discussion about that is in #26227. I agree that it would be nice to do something about this unfortunate name.

[stephentoub]

Right. That discussion is primarily about existing code, though, and how to deal with compatibility. It looks like we're moving the exception type to corelib to enable new uses, such that brand new APIs throw this; I'm suggesting we take this opportunity to move ahead on something that can be used with new APIs before we increase the proliferation of "Win32" things in cross-platform code.