Color interpolation in OKLab, OKLCH spaces for UI gradients

[ickshonpe]

Objective

Add support for interpolation in OKLab and OKLCH color spaces for UI gradients.

Solution

• New InterpolationColorSpace enum with OkLab, OkLch, OkLchLong, Srgb and LinearRgb variants.
• Added a color space specialization to the gradients pipeline.
• Added support for interpolation in OkLCH and OkLAB color spaces to the gradients shader. OKLCH interpolation supports both short and long hue paths. This is mostly based on the conversion functions from bevy_color except that interpolation in polar space uses radians.
• Added color_space fields to each gradient type.

InterpolationColorSpace might be a bit long, might change it to InterpolationMethod or something.

Testing

The gradients example has been updated to demonstrate the different color interpolation methods.
Press space to cycle through the different options.

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Showcase

[alice-i-cecile]

New InterpolationColorSpace enum with OkLab, OkLch, OkLchLong, Srgb and LinearRgb variants.

Why do we need this rather than using Color? Or a generic type with the appropriate trait bound?

[ickshonpe]

New InterpolationColorSpace enum with OkLab, OkLch, OkLchLong, Srgb and LinearRgb variants.

Why do we need this rather than using Color? Or a generic type with the appropriate trait bound?

The enum is just mapped to a constant that is sent to the shader, so using an enum seemed simplest. For polar color spaces you need to choose a path, so using a color type as a discriminator wouldn't be sufficient.

It would be nicer if this was more unified with bevy_color, ideally I think the gradient types should live in the bevy_color module. The current API based on CSS isn't really suitable for more general use cases though.

[alice-i-cecile]

Sounds good. I'm fine to punt on that , but I would like to move this into bevy_color at some point. Linebender's color crate is also doing similar things for shader color math long-term.