graphics/libplacebo 7.349.0 DragonFly

libplacebo is essentially the core rendering algorithms and ideas of mpv turned into a library. This grew out of an interest to accomplish the following goals:

• Clean up mpv's internal rendering abstraction API and make it reusable for other projects.
• Provide a standard library of useful GPU-accelerated image processing primitives based on GLSL, so projects like VLC or Firefox can use them without incurring a heavy dependency on libmpv.
• Rewrite core parts of mpv's GPU-accelerated video renderer on top of redesigned abstractions. (Basically, I wanted to eliminate stateful APIs like shader_cache.c and totally redesign gpu/video.c)