rotate_grid_angles only works on cubes with 2d coords #3145
Description
At present, since we abandoned the generalisation in 'gridcell_angles'.
iris/lib/iris/analysis/_grid_angles.py
Line 227 in 605ef0c
This is a problem, as it limits useability of 'rotate_grid_vectors':
Either generalise, or document limitation in 'rotate_grid_vectors'