Add regression tests for triangulate faces (quads_convert_to_tris)

Basic test for quads_convert_to_tris
As the operator name in blender is different from the bpy name, the operator name in blender was opted in terms of the blend file collection name as well as the test name. This was done so that new developers in the future can easier understand which operator this corresponds to. Although it might be better to change this to the bpy name so as to be consistent with the rest of the codebase.

Updated blend file should be placed in lib/tests/modeling/operators.blend