argparse: ArgumentOptions.metavar can be an array (#41283)
argparse: ArgumentOptions.metavar can be an array (#41283)

This is essential for useful docs for nargs >= 2.

https://docs.python.org/dev/library/argparse.html#metavar says this
about metavar and nargs:

Different values of nargs may cause the metavar to be used multiple
times. Providing a tuple to metavar specifies a different display for
each of the arguments.
georgemarshall/DefinitelyTyped,georgemarshall/DefinitelyTyped,mcliment/DefinitelyTyped,dsebastien/DefinitelyTyped,dsebastien/DefinitelyTyped,georgemarshall/DefinitelyTyped,markogresak/DefinitelyTyped,georgemarshall/DefinitelyTyped