Allow opt out of multiple arguments per option flag #1077
Description
The old parser used in the .NET CLI had behavior such that to specify multiple values for an option you had to include the option flag before each one:
--source source1 --source source2 argument
With System.CommandLine, we're able to specify options one after another without re-specifying the option flag:
--source source1 source2 argument
This creates confusion in the following case:
--source source1 argument
With existing CLI behavior, argument is treated as a command level argument whereas with existing system command line behavior it's treated as another argument to the --source option. It would be great is there's a way to opt out of this behavior to avoid breaking changes to the CLI. cc @jonsequitur