It was only used for toUpper/toLower but always computed in the
constructor, including QString::toLatin1 conversion and allocations.
This needlessly slows down all other uses, including supposedly "cheap"
operations QString::toDouble, or accesses inside QResourceFileEngine.
The benchmarks indicates that doing it always when needed is bearable.
There's still a lot of improvement potential on these code paths.
Change-Id: I88b637ee11f9f7ea614f8da4ec5df0bf40664fce
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
