Rethink core-graphics dependency

[kvark]

core-graphics is already at 0.2x version, it breaks often. Is it a part of your public API? Then you'd need to release as often as it does, otherwise clients (e.g. winit) would get duplicated dependencies.

Does it need to be enabled by default?

[kvark]

Ideally, you'd use https://docs.rs/core-graphics-types/0.1.1/core_graphics_types/ instead of core-graphics