This commit is a work in progress...

CMD quoting is weird - It appears to be necessary to preserve whitespace
but you can't disable variable expansion from within quotes (evidenced
by the removal of `_common.cjs` line 68 to 70).

The main progress of this commit is that it fixes the incorrect escaping
of `%` when quoting for CMD. However, it lacks whitespace preservation
which should really be kept - and, to reiterate, whitespace preservation
is impossible without quoting in CMD, as far as I'm aware.

(and correct `getExpectedOutput`  for Unix shells.)

Turns out quoting is necessary in CMD for one important reason: to
prevent argument splitting.

The side affect of quoting whitespace seems to be that, in contrast to
escaping for interpolation, double quotes must be escaped differently.
Hence, this commit also re-introduces the `escapeArgForQuoted` function.
This particular escaping gets a bit confusing when a pre-existing quote
is next to a whitespace character because the inserted quotes from the
actual quoting have an effect on those pre-existing quotes, so they need
to be handled separately.

- Include cases where there's multiple for CMD.
- Cover the caret character (`^`) when quoting for Windows.

These cases are based on uncaught mutants.

Per the new quoting strategy for CMD, quoting does not necessarily mean
the resulting string has a quote character at the start and end of the
string. Thus, remove all such checks from the tests.