Blender Git Loki

EEVEE: Renderlayer artifacts

When rendering the Subsurface scattering lighting render layer with high
sample count render artifacts can appear. This patch will remove these
render artifacts by using a more precise texture format when samples
will be larger than 128. As with the new eevee-shadows it is more common
to use higher number of samples.

The reason why it was visible in the subsurface scattering is that every
sample could change the color. Adding different values will reduce
precision over the number of samples.

The subsurface color render layer also has this issue, but it is not noticeable as
the colors tend to be close to each other so the colors would
most of the time just shift the precision and hold up better.

Reviewed By: fclem

Differential Revision: https://developer.blender.org/D6245