qt: fix pip player can not be dragged if it overlaps flickable view delegate

I have observed this bug on both Qt 6.2 and 6.8. Flickable somehow steals the drag if PIP player overlaps with the view's delegate. To reproduce it, try to scroll the view to the middle/center first before dragging the pip player.

I think this is a Qt bug. But we can fix it like this, too.

I have used the old commits from !4357 (merged) (https://code.videolan.org/videolan/vlc/-/merge_requests/4357?commit_id=04295b94ef752a0663144009dd7862d37108cd7e&diff_id=748643#note_442982) that we decided to not use due to increased complexity (they were used to disable flicking with non-touch devices).

This also prevents flicking with non-touch devices.

I have tested on both Qt 6.2 and Qt 6.8.

Request review @chub.