Make click decorators not modify the type

[euresti]

Basically work around python/mypy#3924

[gvanrossum]

I think this introduced a regression. I see code like this:

@click.command()
@click.option("--dump_file", required=True, help="the MySQL dump file to import")
@click.option("--decompress", is_flag=True, default=False, help="decompress dump file")
def cli(dump_file, decompress):
    ...

if __name__ == "__main__":
    cli()

This used to work but now I get

 Too few arguments for "cli"

on that line line.

[euresti]

Oh I see. click.command doesn't return f it returns a Command object

[euresti]

Fix here: #2331