[feature request] user defined priorities of automatic threading layer choice #4486

Feature request

In https://numba.pydata.org/numba-doc/dev/user/threading-layer.html, it is shown how to select the 3 available threading layers.

This feature request concerns setting relative priorities between this 3 threading layers. i.e. I still want Numba to automatically choose one for me, but I want to specify the priorities between them. For example if the first is not available, fall back to lower priority ones.

The priority I want to set is 'omp', 'tbb', 'workqueue'. By the way, is the current behavior having the priority of 'tbb', 'omp', 'workqueue', i.e. tbb is chosen first, and if not available fall back to omp, etc.?