* Remove argument separator from commands
Currently, the argument separator (`--`) is only supported on
`dotnet run`. This PR removes it from other commands to make the help and
usage of these command clearer.
* Adding dotnet run message test
* Responding to PR feedback
- Ensure the long names start with `--`
- Handle null strings in UnescapeNewlines
- Handle bool options correctly.
- Allow dotnet run, compile-csc, and compile-fsc to handle .rsp files.
Also removed the dependency on Microsoft.Extensions.CommandLineUtils.Sources NuGet package and instead just checking the source files into our repo as internal classes.
Fix#2526