Fix API flaw for QImage::mirror and QImage::mirrored

I suppect newly (Qt6) introduced mirror function was made like mirrored to be similar, but to be very honest believe this is a step in the wrong direction. We ought to deprecate the existing mirror functions and use Qt::Orientations as arguments instead.

Motivation: That something has been a wrong way for a long time is not a reason not to fix it (when it is very wrong) and I had a codereview in some code using QImage::mirror and the result is unreadable code. Now, I didn't think exactly this, but I believe it will be prefectly acceptable to think the below:

void someFunction(QImage &img) 
{
  img.mirror(true); // Now the image is mirrored, right
  callSomeOtherFunction(image);
  img.mirror(true); // We ensure image is still mirrored (in case the above function changes something)
  callAthridFuncttion(image); 
  img.mirror(false); // Ensure the image isn't mirrored anymore
  // do something more
}

I suggest that the API for mirror (and mirrored) is changed to use Qt::Orientations and that the existing mirror versions are deprecated (lastest in Qt7 and later removed - preferable in Qt7 but latest in Qt8).