Slider: handle scrolling
The Plasma and QtWidgets sliders do this too; qqc2-desktop-style Sliders should do the same for consistency, especially now that there's no longer a conflict between scrollable controls and any scrollable view they may live on.
Implementation is more or less copied from ComboBox.qml.
BUG: 417211 FIXED-IN: 5.91
Edited by Nate Graham