Fix division by zero when `BKE_bone_parent_transform_invert()` inverts a
scale vector with zero components.
Zero values in the to-be-inverted vector are now simply skipped, i.e.
remain zero after inversion. This at least ensures that
`invert_v3_safe(invert_v3_safe(vector))` results in the same vector.
This commit does NOT fix the conceptual problem that an inversion of a
potentially non-invertible vector is relied upon. It just avoids the
division by zero.
And make them part of the blender_test runner. The one exception is blenlib
performance tests, which we don't want to run by default. They remain in their
own executable.
Differential Revision: https://developer.blender.org/D8498
