This patch implements the Fog Glow Glare node by porting the CPU
implementation, so it is not GPU accelerated and is not expected to be
realtime. However, after d4bf23771d, it is now fast enough to be usable,
see that commit for more information on the implementation.
The only difference is that the kernel part of the convolution is cached
in the realtime compositor, so it should be about 30% faster than CPU
for interactive editing.
In the future, this implementation will be replaced by a proper GPU
implementation, likely based on VkFFT.
f0c379e1d3