EEVEE-Next: Depth Of Field: Port implementation to compute shader

This is a port of the previous implementation but using compute
shaders instead of using the raster pipeline for every steps.

Only the scatter passes is kept as a raster pass for obvious performance
reasons.

Many steps have been rewritten to take advantage of LDS which allows faster
and simpler downsampling and filtering for some passes.

A new stabilize phase has been separated from another setup pass in order
to improve it in the future with better stabilization.

The scatter pass shaders and pipeline also changed. We now use indirect
drawcall to draw quads using triangle strips primitives. This reduces
fragment shader invocation count & overdraw compared to a bounding
triangle. This also reduces the amount of vertex shader invocation
drastically to the bare minimum instead of having always 3 verts per
4 pixels (for each ground).

release/scripts/startup/bl_ui/properties_render.py

@@ -223,7 +223,7 @@ class RENDER_PT_motion_blur_curve(RenderButtonsPanel, Panel):
 class RENDER_PT_eevee_depth_of_field(RenderButtonsPanel, Panel):
     bl_label = "Depth of Field"
     bl_options = {'DEFAULT_CLOSED'}
-    COMPAT_ENGINES = {'BLENDER_EEVEE'}
+    COMPAT_ENGINES = {'BLENDER_EEVEE', 'BLENDER_EEVEE_NEXT'}
 
     @classmethod
     def poll(cls, context):