Add option to tint spot light with cookie color

[mpmxyz]

Is your feature request related to a problem? Please describe.

Imagine you want to create a realistic video projector to project an image at a wall. The Light component with LightType "Spot" has the capability to shape the cone of light with a a "cookie" texture. Unfortunately this only reads the alpha channel of the texture.

Describe the solution you'd like

To preserve existing content there should be a non-default mode that respects the RGB of the given cookie.

Describe alternatives you've considered

The user I met who attempted this used three cameras to render tints of the video texture. They were still struggling to convert brightness to transparency, though.

Additional Context

No response

Requesters

No response

[TisFoolish]

To preserve existing content there should be a non-default mode that respects the RGB of the given cookie.

Alternatively, any lights with cookies from before this change would get marked as "alpha only".

It all depends on what should be default, alpha only or full color

[Geenz]

I've thought about doing this while we're still on Unity (it's not super difficult, but the effort is still considerable), but we're more likely to contribute something upstream to bevy for something like this and handle it in Sauce.

[lxw404]

I'd much rather see this behavior in Sauce tbh. Not having to create 3 separate light cookies for RGB -> 3 alpha channels would be an instant win for creative lighting and video projectors.

[shiftyscales]

Marking this as something to look into / consider following #1401.