get_polar_eq method for Machine

[BonneelP]

Some model (like Subdomain) require to have a polar approximation of the machine. It would be great to have a get_polar_eq method in the Machine class. This method will return an equivalent machine object but with the polar versions of the laminations (by calling a get_polar_eq method). It would require a get_polar_eq for each kind of lamination.

For LamSlotWind, the method is simple: the method of the slot are defined to compute the polar height, angles... The get_polar_eq method would call the corresponding comp methods and change the slot type to SlotType22 (https://eomys.com/produits/manatee/howtos/article/how-to-set-up-slot-type-22).

Then there are the other type of lamination (we can create the method and use "NotImplementedYetError" from pyleecan.Methods by waiting) that need to be defined.

[BonneelP]

The first part of the get_polar_eq have been added in 937384d9f29ecc98db04c3c5a61b2b81b3e451a9