This patch mixes the alpha channel of the color in the Mix mode of the
Mix node. This has no effect on EEVEE/Cycles since they do not support
alpha, but affects the Compositor, Geometry Nodes, and Texture Nodes.
Previously, the alpha of the first color was assumed, which meant mixing
two images with transparency using a mask in the compositor resulted in
part of the image having bad alpha and required manually mixing of the
alpha channel. And this is the main motivation of this patch.
Pull Request: https://projects.blender.org/blender/blender/pulls/146461
2f745308ed