Test not only `xarray` inputs, but also `xtensor` and `xtensor_fixed`.
These are currently failing.

Also test some more cases with `column_major` inputs.

An `xaxis_slice_iterator` always refers to a 1d view, so just use an
array of size 1 for the shape and stride.
Another type would probably be more optimal in case of compile-time
fixed size (e.g. `xtensor_fixed`), but at least this is correct.

Always use runtime dimensionality `xaxis_iterator` shape and strides.
Other types would probably be more optimal in case of compile-time
fixed dimension and/or size (e.g. `xtensor`, `xtensor_fixed`), but at
least this is correct.