Vstest: Add autogenerated header for generated program.cs

[codito]

Generated Program.cs should have a header similar to other auto generated files. This will allow static analysis tools to ignore this file.

// <auto-generated> This file has been auto generated. </auto-generated>

or:

//------------------------------------------------------------------------------
// <auto-generated>
//     This code was generated by a tool.
//     Runtime Version:4.0.30319.42000
//
//     Changes to this file may cause incorrect behavior and will be lost if
//     the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------


// Generated by the MSBuild WriteCodeFragment class.

Original issue:
https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/2282
https://github.com/dotnet/roslyn/issues/16856

[codito]

Requires a modification in logic here: https://github.com/Microsoft/vstest/blob/master/src/Microsoft.NET.Test.Sdk.targets#L42

[martincostello]

@codito Happy to do a PR to fix this now that I know where the change needs to go.

[codito]

@martincostello thanks a lot!