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: #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 #51335.

---------

Co-authored-by: Matt Bauman <[email protected]>

Author: adrhill

NEWS.md

@@ -116,6 +116,7 @@ New library features
   the uniquing checking ([#53474])
 * `RegexMatch` objects can now be used to construct `NamedTuple`s and `Dict`s ([#50988])
 * `Lockable` is now exported ([#54595])
+* `Base.require_one_based_indexing` and `Base.has_offset_axes` are now public ([#56196])
 * New `ltruncate`, `rtruncate` and `ctruncate` functions for truncating strings to text width, accounting for char widths ([#55351])
 * `isless` (and thus `cmp`, sorting, etc.) is now supported for zero-dimensional `AbstractArray`s ([#55772])
 

base/public.jl

@@ -28,6 +28,10 @@ public
     acquire,
     release,
 
+# arrays
+    has_offset_axes,
+    require_one_based_indexing,
+
 # collections
     IteratorEltype,
     IteratorSize,

doc/src/base/arrays.md

@@ -115,6 +115,12 @@ Base.checkindex
 Base.elsize
 ```
 
+While most code can be written in an index-agnostic manner (see, e.g., [`eachindex`](@ref)), it can sometimes be useful to explicitly check for offset axes:
+```@docs
+Base.require_one_based_indexing
+Base.has_offset_axes
+```
+
 ## Views (SubArrays and other view types)
 
 A “view” is a data structure that acts like an array (it is a subtype of `AbstractArray`), but the underlying data is actually