Add BuildTools publish step tasks and dependencies

Add BuildTools publish step tasks and dependencies

Copies the closure of C# code from the BuildTools repo that's necessary for the Core-Setup publish tasks. There are no changes except automatically removing and sorting the using statements.

Source: https://github.com/dotnet/buildtools/tree/dotnet/core-setup@55d43483866c7caeeace96355add3a9b12fa5795

Using the existing BuildTools code reduces the risk of behavior differences vs. trying to find equivalents in Arcade. The upcoming new Arcade-powered publish functionality makes short-term effort to deduplicate these tasks throwaway work.

Commit migrated from https://github.com/dotnet/core-setup/commit/ea269ba71cc53b8bf217f20953fcbad85647033b