Add GitHub Actions for tests

[rstm-sf]

Hello!

Add GitHub Actions for tests

• [x] Upgrade tfm for core
• [x] Add actions script
• [x] Fix tests (in fact they are solved, but they are not solved and these are separate problems #34 )
• [x] Fix runners tests for net47 on VS

Can also close_ #33

[rstm-sf]

* Fix runners tests for `net47` on VS (or separate PR)

This was partially solved.

It turned out that when running the test from studio BaseDirectory from AppDomain.CurrentDomain is equal to this path C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\Common7\IDE\Extensions\TestPlatform\

For CecilNetstandardTests and CecilTests this can be solved with something like

AppDomain.CurrentDomain.AssemblyResolve += (s, e) =>
{
    var name = e.Name.Split(',').First() + ".dll";
    return Assembly.LoadFile(Path.Combine(selfDir, name));
};

But XamlParserTests depend on this https://github.com/kekekeks/XamlX/blob/697a419675a8055b7ef9a1904360359522b30616/tests/XamlParserTests/CompilerTestBase.cs#L77

or this https://github.com/kekekeks/XamlX/blob/697a419675a8055b7ef9a1904360359522b30616/src/XamlX/IL/SreTypeSystem.cs#L27

which ultimately raises an exception like this https://github.com/kekekeks/XamlX/blob/697a419675a8055b7ef9a1904360359522b30616/src/XamlX/TypeSystem/TypeSystem.cs#L303

[rstm-sf]

* Fix tests

This actually works too, but dotnet test doesn't like it https://github.com/rstm-sf/XamlX/pull/3/checks#step:9:22

But it doesn't really work anywhere. I think need to think about it

or this

https://github.com/kekekeks/XamlX/blob/697a419675a8055b7ef9a1904360359522b30616/src/XamlX/IL/SreTypeSystem.cs#L27

[rstm-sf]

This actually works too, but dotnet test doesn't like it https://github.com/rstm-sf/XamlX/pull/3/checks#step:9:22

#34

I believe adding the github actions is done. It looks like they are disabled here

[rstm-sf]

@kekekeks hello, does it make sense to update it?