tests: add a helper to stress test argument quoting

tests: add a helper to stress test argument quoting

On Windows, we have to do all the command-line argument quoting
ourselves. Worse: we have to have two versions of said quoting, one for
MSYS2 programs (which have their own dequoting rules) and the rest.

We care mostly about the rest, and to make sure that that works, let's
have a stress test that comes up with all kinds of awkward arguments,
verifying that a spawned sub-process receives those unharmed.

Signed-off-by: Garima Singh <garima.singh@microsoft.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>