EEVEE Film accumulation workaround for Metal/Intel iGPUs.
On Metal the Intel iGPUs do not support image read write
on array textures. However this limitation doesn't show
any artifacts when using the compute shader.
This PR is a work around that uses the film_comp shader
to process the film samples, but uses a separate film_copy_frag
shader to read the result and copy them to the frame buffer.
I deliberately didn't include the fix to the film_frag shader
as that would change the read/write resources and could lead
to performance issues for other platforms. Writable resources
are typically slower compared to read only resources.
Some code needed to be duplicated (and not added to `*_lib.glsl`)
as compilers would still raise compilation errors due to imageStore/Load
on incompatible resource access.
The Metal/Intel iGPU is also marked to have limited support as
raytracing and probes still produces big artifacts.
This workaround can be tested on any platform just by setting
`use_compute_ = true` in `Film::sync`
Related to #122361
Pull Request: https://projects.blender.org/blender/blender/pulls/123330
c525c0354f