Library has odd behavior if a user defined version flag is specified

Was converting an old app that had a --version flag to System.CommandLine. It seems that there's also a --version flag integrated into System.CommandLine, which was taking precedence. System.CommandLine should error if one of the specified root options interferes with one of the built in options.

Start by reproducing the reported behavior in a System.CommandLine app that defines a root --version option, then trace the code that registers and resolves built-in options. Done means the library reports an error when a user-defined root option conflicts with a built-in option, with coverage for the --version case.

Scritto dal modello di indicizzazione a partire dal testo della issue.