bevy_color: migrate color conversion code from bevy_render

[viridia]

Currently, bevy_color uses color conversion functions contained in bevy_render. This means that bevy_color depends on bevy_render. This dependency should be the other way around - bevy_color should be a lower-level dependency of bevy_render.

To fix this, a number of modules will need to be moved:

• The colorspace module in bevy_render should be moved to bevy_color.
• The From impls that convert between the old legacy color type to the new color types should be moved to bevy_render.

[CptPotato]

Side question: With this change, is bevy_render's dependency on bevy_color even needed, or could it simply use wgpu::Color?

[viridia]

An example where bevy_render uses color is ClearColorConfig. This needs to be a type which can easily be converted from a color via .into().

Also, it looks like wgpu::Color uses f64, which seems like overkill for Bevy rendering pipelines.