Add support for ExecuteMain() where Main matches the signature of C# entry point

Add an execute Main that takes a `Func` and `param string args` and returns both the func return and the console output (yes, the best way to return both is a dilemma.

Start by reading the existing ExecuteMain entry point and how Main-style console applications are currently invoked. Clarify the expected behavior for a Func plus param string args, especially how the function return value and console output are represented together; done means ExecuteMain supports that signature and exposes both results.

Written by the indexing model from the issue text.