This seems to be the only way to fix using this class, which is
fundamentally incompatible with high DPI support, with bitmaps of
different logical but identical physical sizes.
By using physical size we ensure that the code chopping up the provided
bitmap in multiple images doesn't do it with the bitmap having the same
physical size but a different logical size from all the other bitmaps.
And, conceptually, logical size of the bitmaps in it really shouldn't
matter to the image list as it doesn't have a scaling factor and so
can't do anything useful with the logical size.
Moreover, we can't add wxImageList::SetScaleFactor() neither because
this class is, by design, supposed to be shareable between different
controls which may use different scale factors, so it doesn't make sense
to speak of the scale factor of the image list itself.
This undoes the changes made in the generic implementation back in
c374eefd34 (Fold wxOSX-specific wxImageList into generic version,
2018-10-30) and also eb52e86553 (Take into account scale factor of
images added to wxImageList, 2021-04-03).
Also update a couple of places where wxImageList is still used to use
physical sizes. Unfortunately some others can't be easily fixed, e.g.
global wxFileIconsTable would have to be completely rewritten.
Finally, add a unit test checking that things work as expected now:
previously the size of 24x24 bitmap in the image list containing
(scaled) 32x32 bitmaps would be 21x21 due to sub-bitmap extraction
kicking in.
Closes#23994.
53b4f4ddf2