Merge branch 'master' into soc-2020-io-performance

Create test OBJ files in temporary place.

Merge branch 'blender-v2.93-release'

Fix T86805 Inconsistent results for exact boolean.

The fast triangulator from Blenlib could leave a non-manifold mesh
after removing degenerate triangles. Switched to an exact triangulator.

Fix test to not use Ankit's directory name.

Merge branch 'master' into soc-2020-io-performance

Fix T86879 Boolean exact crash with dependency loop.

When boolean's Object also has a modifier that depends back on
the target Object, a crash occurred.
In a case like this, BKE_modifier_get_evaluated_mesh_from_evaluated_object
returns NULL, so just have to protect against that case.

Progress towards making material output the same as the python exporter.

The python exporter was stricter about what Principled BSDF node it
would use -- it only wanted one directly attached to the Material Output.
Also, the Python exporter sets the ambient to (1,1,1) if no reflections.
And there was a mistake in how the C++ exporter set the illumination model.

Also printed out the components in the same order as the python one,
for easier comparison.

Fixed problem of repeated same materials output in MTL file.

The code was writing out all of the materials for each object.
Refactored so that the materials for all objects are gathered
together, deduping, and writing out at the end of a frame.

Fix a bad default assignment and an unused parameter.