platformtheme: Add hints for FlickMaximumVelocity and FlickDeceleration
THIS PR DOES NOT WORK AS IS, THESE SETTINGS ARE NOT EXPOSED BY QT: https://bugreports.qt.io/browse/QTBUG-121500 Fixed by https://codereview.qt-project.org/c/qt/qtdeclarative/+/548039
In https://codereview.qt-project.org/c/qt/qtbase/+/91242 these hints were introduced to customize Flickable scrolling.
In the process, they changed the Flickable deceleration speed from 1500 -> 5000 pixels/sec which is far too high in my opinion, removing inertia from touchscreen and trackpad scrolling. Here we specify the old value as the default.
Edited by Devin Lin