Feature request: Rename _indsstring to indsstring and allow packages to define methods for it

[jishnub]

The function _indsstring is used to convert an axis to a string representation in array summaries, and has special methods defined for Base.IdentityUnitRange and Base.Slice. The leading underscore seems to indicate that this is for internal usage. However this is a useful function that other packages that define custom axis types might use too, eg. OffsetArrays. Would it make sense to rename it to indsstring and allow packages to extend this? A search on juliahub indicates that currently this is not being used by any package.