We now reuse 9 hitpoints from the neighboorhood using a blue noise
sample distribution as mentionned in the reference presentation.
Reusing more rays does however make some area a bit more blury.
The resulting noise is quite lower compared to previous implementation
which was only reusing 4 hits.
This split is to make code easier to manage and rename the files to
`effect_reflection_*` to avoid confusion.
Also this cleans up a bit of the branching mess in the trace shader.
