This new class mirrors the existing QLocaleXmlWriter and places the two side-by-side in qlocalexml.py, rather than having the writing and reading in separate places. Made judicious use of transformed versions of mappings to save repeated iteration of a mapping's entries to do lookups on fist entries of pair-values; several (id, name, code) data-sets are sometimes indexed by id, sometimes by name. Reworked the default_map, that the complicated compareLocaleKeys() used in sorting locale keys, to map IDs instead of names; the function also needed the locale_map so that it could convert IDs to names, which we can skip by going directly with IDs. Task-number: QTBUG-81344 Change-Id: Iff6a97f7f0755b56dda70d8a6796ec074c558910 Reviewed-by: Cristian Maureira-Fredes <cristian.maureira-fredes@qt.io>