Allow temporary VM mouse capture with user consent

[DemiMarie]

Qubes OS version
Qubes release 4.0 (R4.0)

Affected component(s) or functionality
Mouse virtualization

Brief summary
Minecraft is not playable in an AppVM. The graphics work fine, but I can’t aim the camera.

Others have reported no such problems, and I believe that this may relate to QubesOS’s mouse virtualization, so I am reporting this as a QubesOS bug

To Reproduce

1. Create a new Debian-based TemplateVM or StandaloneVM
2. Purchase Minecraft (Java edition)
3. Install the official Debian package for Minecraft.
4. Try to play

Expected behavior
It works, albeit with slow frame rate due to the lack of hardware-accelerated graphics.

Actual behavior
I cannot get the camera to move vertically in any controllable way, rendering the game unplayable.

Screenshots
I don’t have any, but can provide them if they would be helpful.

Additional context
This could be an issue with the Linux touchpad drivers, but I doubt it.

Solutions you've tried
USB pass-through of a USB mouse.

[zaoqi]

Minetest also has this problem.

1. Create a Fedora 30-based VM.
2. $ dnf install minetest
3. $ minetest

[biergaizi]

I suggest removing "for full-screen applications" from the title - allowing mouse capture is also useful in non-fullscreen applications. For example, CAD packages, such as KiCad or LibreCAD, heavily relies on mouse capture for navigation. Without a mouse capture, it's almost impossible to use any 2D CAD programs in Qubes.