Config-less CoreCLR and improved runtime load message

[filmor]

What does this implement/fix? Explain your changes.

• Bump clr-loader dependency to 0.2.0 and adjust interface, allows to load a .NET Core Python.NET by just setting PYTHONNET_RUNTIME=coreclr or from pythonnet import set_runtime; set_runtime("coreclr")
• Improve error message if the runtime fails to load

Does this close any currently open issues?

#1868

Checklist

Check all those that are applicable and complete.

• Make sure to include one or more tests for your change
• If an enhancement PR, please create docs and at best an example
• Ensure you have signed the .NET Foundation CLA
• Add yourself to AUTHORS
• Updated the CHANGELOG

[filmor]

@lostmsu Do you have any idea why this one doesn't run the CI?

/edit: Sure, now it does :)

[lostmsu]

Can you point to the corresponding change in clr_loader?

[lostmsu]

I take it it is this one: pythonnet/clr-loader#31

[filmor]

Meh, I'll have to test it tomorrow on a Windows machine, not really sure what I broke there (and why it works for the clr-loader CI).

[lostmsu]

Have you seen the cause of the exception?

OSError: cannot load library 'c:\hostedtoolcache\windows\python\3.7.9\x64\lib\site-packages\clr_loader\ffi\dlls\amd64\ClrLoader.dll': error 0x7e. Additionally, ctypes.util.find_library() did not manage to locate a library called 'c:\hostedtoolcache\windows\python\3.7.9\x64\lib\site-packages\clr_loader\ffi\dlls\amd64\ClrLoader.dll'

The above exception was the direct cause of the following exception:
...

[filmor]

Have you seen the cause of the exception?

OSError: cannot load library 'c:\hostedtoolcache\windows\python\3.7.9\x64\lib\site-packages\clr_loader\ffi\dlls\amd64\ClrLoader.dll': error 0x7e. Additionally, ctypes.util.find_library() did not manage to locate a library called 'c:\hostedtoolcache\windows\python\3.7.9\x64\lib\site-packages\clr_loader\ffi\dlls\amd64\ClrLoader.dll'
The above exception was the direct cause of the following exception:
...

Nope, didn't see that one. Then I must have broken the wheel building somehow. I can see that the wheel does not include the file at all right now. So, 0.2.3 it will be ;)

[DareDevilDenis]

Hello. Does this change cause the following issue: pythonnet/clr-loader#35
See question: #1951