Make `no_offset_view` public

[JeffFessler]

The readme refers to OffsetArrays.no_offset_view, suggesting that no_offset_view is a method that developers can use. It would be nice to make it public so developers can count on it.

[JeffFessler]

I'd be happy to make a PR but thought maybe I should wait to see what happens with
#385
since decisions about what methods are public probably belong with that effort.