Don't build if used any of not supported API

[montyclt]

The Blazor FAQs says:

Yes, the .NET runtime used for Blazor supports .NET Standard 2.0. APIs that aren't supported in the browser throw Not Supported exceptions.

There are any list with unsopported APIs of the .NET Standard? Can a MSBuild task used to interrumpt the build and mark as error if any of this APIs are used instead of detect the error in execution time when the exception is thrown?

[danroth27]

We don't have the precise list yet of the .NET Standard APIs that will work in Blazor. A lot of APIs already work today. Some APIs will work, but haven't been implemented yet. Others will never work because of the constraints of running in the browser. I can imagine us shipping an analyzer that provides a build time experience for detecting usage of APIs that won't work.

[pranavkm]

/cc @lewing. Having the portability analyzer would help here.

[marek-safar]

This requires dotnet/designs#110 approval