[libc++] Granularize <__locale> into __locale_dir (#213667) The <__locale> header was a collection of distinct utilities. This patch splits it up into granular headers under __locale_dir/. This patch however does not use the granular headers from users of <__locale>: this will be done in a separate patch. Assisted by Claude GitOrigin-RevId: c703445771082920ce7cc13d75d721074539f914