API/DEPR: Index.view _typ check, return type

[jbrockmendel]

Index.view has a cls argument (instead of dtype, which I would expect) and starts with:

        # we need to see if we are subclassing an
        # index type here
        if cls is not None and not hasattr(cls, "_typ"):

The "_typ" check must have been intended to catch types defined in pd.core.dtypes.generic, but it isn't clear to me why we do that.

Let's just have view take a dtype keyword like Series.view.

update: also it sometimes returns an Index and other times an ArrayLike. let's choose just one.

[jorisvandenbossche]

Or deprecate it, like we want to do for Series (#20251), and only keep it on the array level?