[[ HiDPI ]] Add usePixelScaling property to enable / disable pixelScaling
[[ HiDPI ]] Add execution errors for invalid setting of pixelScale, usePixelScale properties
[[ HiDPI ]] Add MCResPlatform* functions to query per-platform for pixel scaling capabilities
[[ HiDPI ]] Revise per-platform update after changing pixel scale settings
[[ HiDPI ]] Implement refactored pixelScale on iOS. Implement usePixelScaling on iOS
[[ HiDPI ]] Fix typo in OSX MCScreenDC::platform_displayinfocacheable() signature