Port away from KStatefulBrush::brush(const QWidget*)

Soon to be deprecated, use the QPalette overload instead.
2 jobs for master in 30 minutes (queued for 147 minutes and 5 seconds)
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  Build
passed build_clazy_clang_tidy #113963

00:14:30

passed linux kf5-qt5 qt5.15 #113962

00:15:30

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