Blender Git Loki

Fix T93352: Material previews lost render samples

There are few layers of things which lead to the situation
of more noisy material preview: the do-version of the
preview.blend did not happen (at least from the Python
side as we did not investigate the C side deep). This made
Cycles to use default integrator settings for the preview
file ever since the Cycles X was merged. Those settings are
adaptive sampling with max 4K samples, noise threshold 0.01.
Opening the file in Blender 3.0 for edit did run the versioning
code which effectively lowered the number of samples used for
rendering.

This change makes it so the preview file is configured with
the exact effective settings as seen by Cycles prior to the
file was re-saved (adaptive sampling with the parameters noted
above).

This fix does not chaneg the fact that the versioning code is
not used for preview.blend, it only solves the regression in
the quality of previews.

The fix is done and reviewed with collaboration with Dalai and Sergey.