Mostly to pave the way for moving the class code to a file of its own,
but this incidentally saves the need to std::as_const() every use.
Moving the underlying object to a local static of a private method
also saves the need for heap allocation (which was leaked).
Pick-to: 6.6 6.5
Task-number: QTBUG-111228
Change-Id: I30f4bf3c46d39e04d0ac4e3e9ba431945ebb9193
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Ville Voutilainen <ville.voutilainen@qt.io>
d57a78657e