Mac: events root location points vs pixels retina/scale

[7890]

In the mac.m implementation, there are many events having

const NSPoint           rloc = [NSEvent mouseLocation];

By default, NSEvent.mouseLocation returns coordinates in points (logical units), not physical pixels.
I think it would be correct to account for the backing store scale factor.
Because it touches many methods, I would like to get some thoughts @drobilla beforehand. On Mac with retina, all sizes should be 'real' in that they reflect the pixel count, not the points, which is from what I see the case for most things (e.g. view size). Is this reasonable?

[drobilla]

You can see that this is not the case with any of the example programs, e.g. pugl_shader_demo makes a 512x512 window and the mouse events match.

The general idea is indeed that everything should be real physical pixels on all platforms (although that has its problems, see #108)