Mark `require_one_based_indexing` and `has_offset_axes` as public (#56196)
The discussion here mentions `require_one_based_indexing` being part of
the public API: https://github.com/JuliaLang/julia/pull/43263
Both functions are also documented (albeit in the dev docs):
* `require_one_based_indexing`:
https://docs.julialang.org/en/v1/devdocs/offset-arrays/#man-custom-indices
* `has_offset_axes`:
https://docs.julialang.org/en/v1/devdocs/offset-arrays/#For-objects-that-mimic-AbstractArray-but-are-not-subtypes
Towards https://github.com/JuliaLang/julia/issues/51335.
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Co-authored-by: Matt Bauman <mbauman@gmail.com>