Create get_positioners_iter
The bliss.common.alias
module contains get_axes_positions_iter
which deals with data fetching and formatting.
Such feature should not be part of such class which is used as the global map.
Instead a get_positioners_iter
was added.
I do not intent to clean up everything, but here is a small step that can be used to release the use of such function.
Related to !5993 (merged)