Fix the unnecessary recreation of the denoiser that occurs if
Cycles had fallen back to an alternative denoiser in a previous
interation. (E.g. Fallback from OptiX to OIDN)
This issue occured because Cycles didn't understand that when it
previously setup the denoising device, that it had fallen back to
something else. So it thinks the denoising settings have been changes
and tries to recreate the denoiser.
The solution is to first compute the settings change due to
the fallback, then check to see if it's different from the current
denoiser, then recreate the denoiser device if neccesary.
Pull Request: https://projects.blender.org/blender/blender/pulls/125453
2d611f7b45