[.NET 6] Replace reflection usage when setting up linker pipeline

[rolfbjarne]

Context:

xamarin-macios/tools/dotnet-linker/SetupStep.cs

Lines 19 to 28 in 92ce997

	List<IStep> _steps;
	public List<IStep> Steps {
	get {
	if (_steps == null) {
	var pipeline = typeof (LinkContext).GetProperty ("Pipeline").GetGetMethod ().Invoke (Context, null);
	_steps = (List<IStep>) pipeline.GetType ().GetField ("_steps", BindingFlags.Instance | BindingFlags.NonPublic).GetValue (pipeline);
	}
	return _steps;
	}
	}

This reflection usage should be removed at some point.

Ref (Android): dotnet/android#4709

[spouliot]

removed with #11739