ArgumentParser: Detect which Parser parsed Result

[satoshin21]

Hi!
I added isBelong(to: ArgumentParser) method to ArgumentParser.Result.
I think this method is needed to detect which subcommand is executed with optional PositionalArgument.

Like this.

let parser = ArgumentParser(...)
let subParser1 = parser.add(subparser: "sub1")
let optionalArgument1 = local.add(positional: "sub1_arg", kind: String.self, optional: true)
let subParser2 = parser.add(subparser: "sub2")

// which subparser is given?
let result = try! parser.parse(Array(CommandLine.arguments.dropFirst()))

If isBelong(to: ArgumentParser) is implemented, We can detect that.

let result = try! parser.parse(Array(CommandLine.arguments.dropFirst()))

if result.isBelong(to: subParser1) {
    // this command is executed by subParser`1`.
}

Or If you have any idea to detect this without above method, Can you let me know?

[tomerd]

thanks for the PR @satoshin21 we are adopting SwiftArgumentParser: #2653 shortly. okay to close?

[satoshin21]

Thank you for letting me know, @tomerd
I close this PR.