argparse: Add required: boolean to SubparserOptions

The required option was added in python 3.7.0a2 as a way to make
subparsers required again (the default behaviour in Python 2.7).

* https://bugs.python.org/issue9253
* python/cpython#3027

Since npm argparse 2.0.1 is a straight conversion of the Python
3.9.0rc1 version of argparse the required flag is valid here too.

Author: tsondergaard

types/argparse/argparse-tests.ts

@@ -179,6 +179,7 @@ const subparserExample = new ArgumentParser({
 const subparsers = subparserExample.add_subparsers({
     title: "subcommands",
     dest: "subcommand_name",
+    required: true,
 });
 
 let bar = subparsers.add_parser("c1", { add_help: true, help: "c1 help" });

types/argparse/index.d.ts

@@ -51,6 +51,7 @@ export interface SubparserOptions {
     dest?: string;
     help?: string;
     metavar?: string;
+    required?: boolean;
 }
 
 export interface SubArgumentParserOptions extends ArgumentParserOptions {