Currently, handling of touch devices in the app grid is a bit awkward,
paging by dragging the view can only happen if started from the gaps
between icons, trying to drag from an icon will trigger DnD, and popping
up the menu takes over it all.
Instead, have the app grid actions play this game of rock-paper-scissors:
- Fast swipes on icons trigger scrolling, beats DnD and menu
- Slower press-and-drag on icons trigger DnD, beats scrolling and menu
- Long press triggers menu, beats scrolling, is beaten by DnD
This allows quick swipes to handle navigation, while still allowing the
fine grained operations. DnD, when triggered, dismisses the menu, if
shown.
This all could probably be nicer with a more stateful gesture framework,
we're not there yet though.
Fixes: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/3849
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1774>
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