Implement GH-10024: support linting multiple files at once using php -l

This is supported in both the CLI and CGI modes. For CLI this required
little changes.

For CGI, the trick

Implement GH-10024: support linting multiple files at once using php -l

This is supported in both the CLI and CGI modes. For CLI this required
little changes.

For CGI, the tricky part was that the options parsing happens inside the
loop. This means that options passed after the -l flag were previously
simply ignored. As we now re-enter the loop we would parse the options
again, and if they are handled but don't set the script name, then CGI
will think you want to read from standard in. To keep the same "don't
parse options" behaviour I simply wrapped the options handling inside an
if.

Closes GH-10024.
Closes GH-10710.

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