SDK resolver should flow traced errors from hostfxr to msbuild

[nguerrera]

Follow up to https://github.com/dotnet/core-setup/issues/6970

As of now, the that is shown in VS when sdk resolution fails is overly generic:

https://github.com/dotnet/cli/blob/6b0885139c1f37093ba4d3797f46fe90bf093883/src/Microsoft.DotNet.MSBuildSdkResolver/Strings.resx#L133

We can set an error writer on hostfxr and then return the more specific errors to msbuild, and ultimately VS.

See https://github.com/dotnet/core-setup/blob/1a10af88e3904b1d9790be38450c23eea683d6ae/src/corehost/cli/fxr/hostfxr.cpp#L391

cc @peterhuene

[nguerrera]

cc @KathleenDollard

[nguerrera]

It would be nice to be able to plumb warnings too, and to have a flag that can be set somehow to get all the informational tracing as well into the binlog, but that is blocked by https://github.com/dotnet/core-setup/issues/6972