ohos: move makeMemoizingSupplier() to qohosutils.h

The memoizing supplier is a generic helper, but it is private to
qohosmimedata.cpp, so no other part of the plugin can use it. Move it
to qohosutils.h, next to the other supplier and consumer helpers.

Task-number: QTBUG-149732
Pick-to: 6.12
Change-Id: I01f4ca6076d2c3e4be0c7a8491e2d97c4b91f62f
Reviewed-by: SanthoshKumar Selvaraj <santhosh.kumar.selvaraj@qt.io>
Reviewed-by: Zbigniew Chyla <zbigniew.chyla@qt.io>