Blender Git Loki

Fix T77893: Crash drawmanager threading custom data

Tangent normals were temporarily saved in the original given layers but
the typeinfo wasn't updated. This lead to several issues since we
changed the threading of the mesh extraction.

This patch stores the tangent normals in a temporary custom data on the
stack this way the typemap doesn't need to be updated.

Still need to run the tests for an hour to see if it is fixed

Reviewed By: Cl�ment Foucault, Philipp Oeser

Differential Revision: https://developer.blender.org/D8095