Instead of duplicating the same code in both,
`QtGraphics::GetResolution` and
`QtSvpGraphics::GetResolution`, create a static
helper method `QtGraphicsBase::ImplGetResolution`
in their base class and call that.
While at it, also move `QtGraphics::GetResolution`
to the source file where all of the other
`QtGraphics` methods are implemented.
Change-Id: I721459e8b65756f214fee77ac4d3cb8e500f0b57
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/170930
Tested-by: Jenkins
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>
