Improve maps

[mscroggs]

The code in maps.h can be sped up and optimised

[mscroggs]

In particular, we should remove this switch:

basix/cpp/basix/maps.h

Lines 133 to 147 in e2137c8

	switch (map_type)
	{
	case maps::type::identity:
	return impl::identity(u, U, J, detJ, K);
	case maps::type::covariantPiola:
	return impl::covariant_piola(u, U, J, detJ, K);
	case maps::type::contravariantPiola:
	return impl::contravariant_piola(u, U, J, detJ, K);
	case maps::type::doubleCovariantPiola:
	return impl::double_covariant_piola(u, U, J, detJ, K);
	case maps::type::doubleContravariantPiola:
	return impl::double_contravariant_piola(u, U, J, detJ, K);
	default:
	throw std::runtime_error("Mapping not yet implemented");
	}

[garth-wells]

See https://github.com/FEniCS/basix/tree/garth/map-function and https://github.com/FEniCS/dolfinx/tree/garth/basix-map-fn on this.

[mscroggs]

Can we close this following #342?

[garth-wells]

Fixed (for now) in #342.

Future work could be to remove the xt::view, which can be slow.