Add support for COMReference items on .NET Core

[AaronRobinsonMSFT]

Steps to reproduce

The following COM sample doesn't build from the dotnet command. It only builds from within Visual Studio.

Command line

dotnet build ExcelDemo.csproj

Expected behavior

The project should build

Actual behavior

There is a failure to find the ResolveComReferences task.

See dotnet/core#2104
See dotnet/samples#487

[dotMorten]

Any update on this? I'd like to be able to build with COM references using a locally-installed .NET Core SDK without putting a dependency on VS2019.