[C++] Split utf8.h to avoid exposing xsimd dependency to the outside #32347
Description
arrow/util/utf8.h exposes both extern functions and inlined functions, the latter being dependent on xsimd. For consumption of the extern utilities from third-party code, we should split it in two so that xsimd does not have to be present when building.
Reporter: Antoine Pitrou / @pitrou
Assignee: Antoine Pitrou / @pitrou
PRs and other links:
Note: This issue was originally created as ARROW-17037. Please see the migration documentation for further details.