Remove support for DotNetCliToolReference

Back in .NET Core 1 and 2, we had a concept called "project tools". These could be declared in the project file using a `DotNetCliToolReference`. These were effectively replaced by local tools in .NET Core 3, and we made it so that [you could not create a project tool targeting anything higher than .NET Core 2.2](https://github.com/dotnet/sdk/issues/3115).

Given that .NET Core 2.2 is long out of support, we should consider removing the code from the .NET SDK which supports creating and consuming these tools. This includes `ProjectToolsCommandResolver`, tasks and targets supporting creating these packages, and possibly more.