Make rendering pipeline more flexible

[ffreyer]

Currently the rendering pipeline in GLMakie is rather strict. As a result buffers needed for ssao and fxaa are always created and post processing always runs. As things get more complex it would be good to make this more flexible.

It should be posible to disable fxaa, ssao, etc for the full scene. This should cause less framebuffers to be created (i.e. only those that are actually needed) and the rendering pipeline to be shorter. It should also cause less framebuffers to be written to in fragment_output.frag. Potentially we also want to change which shaders are used in the primary render, e.g. for deferred shading.

[ffreyer]

Not sure if I should count this as "actionable" or not. My main goal with this is to move control over the post processing actions to Makie Scenes, so that they can define different pipelines. That goal might be pretty big, since it may involve a lot of magic to go from a simplified pipeline in Makie to the necessary buffers and OpenGL operations in GLMakie.

Either way #4150 is the first step to get there