On Windows, reusing/sharing of OPcache instances with different
configuration is not necessarily supported, so we have to make that it
does not happen for the clean scripts, by using `$orig_ini_settings`
instead of `$clean_params`.

The primary motivation to have each test worker running its own console
is to allow the windows_mb_path tests to run in parallel.  A nice side
effect is that this also prevents changing the code page of the
tester's console window (which can even cause its font to be changed).

To be able to do so, we introduce the `create_new_console` option for
`proc_open()`, which might occasionally be useful for other purposes
than testing.

Mostly reindent PHP scripts to spaces.

This is used to indicate that the test should not be changed by
automated formatting changes.

Any existing tests are going to be written under this assumption...

The default PHP executable was not set when no args were provided.

Closes GH-4894.

Otherwise we would try to access an array element of `false`, which
issues a notice as of PHP 7.4.0.  This would happen, for instance, for
bug63447_001.phpt if CGI is not available.