Extract common packagereferences for MSBuild tasks that ship in the SDK

Several projects in this repo build MSBuild task assemblies. They all have clauses in their project file like

https://github.com/dotnet/sdk/blob/39856f4fe0fc4eba6cd5e920bfcef3d16074abca/src/Tasks/Microsoft.NET.Build.Tasks/Microsoft.NET.Build.Tasks.csproj#L83-L85

That serve to keep the .NET Framework task unified with the dependencies that MSBuild has. Unfortunately they can differ.

We should extract the concept of "this project builds SDK MSBuild tasks" to an imported `SDKDeliveredMSBuildTask.props` file that includes the references like that, and import it in the various projects that build tasks.

You can find those projects by searching for `SystemReflectionMetadataToolsetPackageVersion` and other properties to make sure you've found them all.