This was a feature in Qt 4, but the only platform that carried it over
to Qt 5 was Windows, in ab76593f18, and
that's still the situation.
As a first step in possibly implementing this on more platforms, lets
replace the hard-coded check in QWidgetRepaintManager::hasStaticContents
with a proper QPlatformIntegration capability check in the only call site.
Pick-to: 6.7
Change-Id: I2067109f45116cd8c62facf7224cd748f19e845b
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>
cce303b6a7