Any brush that used the `restore_position_from_undo_step` codepath (i.e.
brushes that use `OrigPositionData` to calculate their deformations) had
the possibility to cause artifacts due to the nested tbb parallelization
causing incorrect usage of TLS data.
To fix this we add a call to `threading::isolate_task` to prevent thread
stealing.
Pull Request: https://projects.blender.org/blender/blender/pulls/129020
feaa7bbbcc