[Development] New approach to hi-dpi and coordinate system for layouts in Qt 6

[Jason H]

First let me say that I have no idea what I'm talking about.

That said, given all the times I've used Qt and experienced issues,
I only remember had problems when dealing with fonts, and the Canvas element on IOS. (I think the Canvas still is blurry)
I've used headless Qt for printing charts (remember Qt Charts?) and all the words came out elided. (Qt 5.2 on Amazon AMI). Rendering at 72 DPI worked but 300 DPI was the problem. IN the end I was never happy, I kept the strings short to avoid eliding and scaled the text up while also increasing the DPI. 
Similarly, iOS seemed to have the most font issues. I liked the idea of using point size for text, but it wouldn't ever behave how it should (there were some other issues with not being able to find what size text was, I think this has been fixed)

Given all my problems, I found myself wondering why points vs pixels was so hard? The I figured everything specified in points should be converted to display pixels via device metrics? It's not like devices change DPI, though if you have multiple monitors this assumption may be invalid if the user moves the window to between screens or another screen.