API: Limit assert_*_equal functions in public API
As discussed on today's call. Just adding `assert_extension_array_equal` relative to 0.25.
LGTM Looking at the `assert_extension_array_equal` code, we probably want to dispatch from there to the more specialized asserts for our known extension arrays (categorical, interval, datetime, etc).

Also, do we want to have an `assert_array_equal` that can handle both extension arrays and numpy arrays?