Missing parts of local storage backend implemented:
- fallback mechanism
- removal of all child keys for groups
- variant decoding instead of string decoding
- report AccessError when organization is empty in settings' ctor
Some WASM-specific adjustments to tst_qsettings have also been
introduced.
Task-number: QTBUG-115509
Fixes: QTBUG-115037
Change-Id: I02cde965b11d98a64fc1ecb261d74838c508afd6
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>
63b64084cd