[Enhancement] Improve the rasterization scale / content scale factor

[mattleibow]

Summary

Right now, the ImageHandler on Windows and iOS each need to track the scale of the view - depending on which window/screen it is on. I have added some things in those handlers, but probably should be more generic.

[mattleibow]

And, what about Android? Can the scale change? Maybe with accessibility things?

[mattleibow]

This is probably a Window feature, so if a dev can find the hosting window, then we should have some IWindow.Density property. Right now we only have the DisplayInfo.MainDisplayInfo.Density which assumes 1 monitor... which is already invalid as I not only have 2 mpnitors, I have different densities on each.