Add tablet grabs

[Drakulix]

Alternative to #2696, that actually implements the new grabs.

After fighting with it for a while, I finally got the WeylusCommunityEdition to work with my iPad (though screen capture doesn't seem to work with this one on cosmic?) for testing and of course the first attempt is half-broken.

• Move grabs on SSD
• Resize grabs floating
• Resize grabs tiling
• Menu grabs - might work via tablet tool buttons on hover, but my tablet doesn't send this event
• Zoom grabs (can't really work)
• Pointer emulation for clients not binding wp_tablet
  • libcosmic apps seem to bind the tablet, but not handle it's input, nothing tbd from cosmic-comps side
• Focusing windows with the tablet tool works now

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[ids1024]

Using PointerFocusTarget for tablet tool focus makes sense.

Testing on my Microsoft Surface, Xournal++ and Firefox tablet input seems to be working fine, which generally means this isn't a regression.

I see a couple issues with the new server-side tablet targets.

• Closing a stack using the pen works, but changing the focused stack element doesn't. (Presumably something we want? but not a major bug.)
• Starting an SSD window drag (of a window not in a stack) with the pen works. But the drag continues when the pen is removed from the screen and placed next to the screen again, with no obvious way to end the drag using the pen. And when moving the pointer there's also a pointer grab.
  • Should the drag be finished on proximity out?
  • Probably this should be independent of pointer, and not create a pointer grab?

[Drakulix]

There is one weird bug remaining, where tiled grabs of windows with SSD don't always release properly. Otherwise this should be a major improvement. @ids1024 Can you give this another test?

Once I found that last bug I am gonna do a rebase and then this should finally be good for a proper review and in-depth QA testing.

[hojjatabdollahi]

Not sure if this PR is relevant here, just FYI: pop-os/iced#376

EDIT: Actually I see you've already mentioned it:

libcosmic apps seem to bind the tablet, but not handle it's input, nothing tbd from cosmic-comps side

[ids1024]

SSD drags generally seem to work well now. CSD drags using xdg_toplevel.move don't seem to be working (I can see nautilus calls move but don't get a grab). And stack decorations still seem to need more tablet interactivity, as before. Firefox and Xournal++ still seem fine.

Those aren't really bugs here though since they are existing limitations.

[Drakulix]

SSD drags generally seem to work well now. CSD drags using xdg_toplevel.move don't seem to be working (I can see nautilus calls move but don't get a grab).

Should be working now! Grab validation didn't fully consider tablets yet.

And stack decorations still seem to need more tablet interactivity, as before. Firefox and Xournal++ still seem fine.

Stack decorations are now interactable with both touch and tablet input. You can drag out a window from a stack using a tablet tool as well. :)

[ids1024]

Yep, those things seem to be working now.