Add a component mixer camera component for rudimentary color grading

[marceline-cramer]

I'd like to be able to attach a Mat3 component named component_mixer (or something along those lines) to a camera entity to apply color grading to it. The matrix just takes the RGB components of the framebuffer as input during the compositing step of the render pipeline and outputs processed RGB data. Using this, one can lighten and darken, desaturate and saturate, and tint the resulting image, which I plan to use to enhance the look and atmosphere of day and night cycles or different meteorological states of Flowerpot's outdoor environment.

[marceline-cramer]

I think an example that renders a simple scene and a UI with sliders that modify the different component mixer elements would also be a great addition, not only for demonstration but also so that users can interactively experiment with different configurations for matrices.

[marceline-cramer]

Here's the UI for doing this operation in Gimp: