Allows to bring back old behavior when color and guiding passes are
denoised at the same time. Exposed as a single enum, so that we only
expose combinations which makes sense from configuration perspective.

Possibilities are:

• None. Assumes that the guiding passes are clean. Gives best results without extra processing time (in expense of requiring to have enough samples rendered to give clean guiding passes).
  
  Corresponds to OIDN cleanAux=true and no prefiltering done on the guiding passes.

• Fast. Old behavior, color and guiiding passes are denoised together. This is fastest way of giving denoised result, in the expense of possible loss of details.
  
  Corresponds to OIDN cleanAux=false and no prefiltering.

• Accurate. Use special guiding passes prefilteringbefore denoising color passes. Gives best results in the expense of extra time needed to perform prefiltering. Avoids over-blurring details.
  
  Corresponds to OIDN cleanAux=true and prefiltering performed on the guiding passes.

Feels like descriptions of the property and items can be more clear,
but wouldn't mind having an input from an independent developer :)