This patch implements the Streaks Glare node. Which is an approximation
to the existing implementation in the CPU compositor. The difference due
to the approximation is bearily visible in artificial test cases, but is
less visible in actual use cases. Since the difference is rather similar
to that we discussed in the Simple Star mode, the decision to allow that
difference would probably hold here.

For the future, we can look into approximating this further using a
closed form IIR recursive filter with parallel interconnection and
block-based parallelism. That's because the streak filter is already
very similar to the causal pass of a fourth order recursive filter,
just with exponential steps.