The signal has been emitted also, when the slider position has changed
without a value change (e.g. on QWidget::show() or on resizing).
This patch stops emitting the signal without a value change.
It adds a verification to tst_QAbstractSlider::setValue(), that
valueChanged is not emitted on a no-op value change.
As a drive-by, the patch removes an unnecessary assignment and
changes signal spy constructions to PTMF syntax.
Pick-to: 6.5 6.4 6.2
Task-number: QTBUG-25365
Change-Id: I9932e45d4e680aa53422ca75aa42a16306213a38
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
8b84374892