[client] x11: regrab input devices after resuming from sleep

[quantum5]

This is meant to fix issues with input devices not working after resuming from sleep, as reported on discord. This should only be merged once confirmed to fix the issue.

To test this, install the bleeding edge host application and apply this PR as a patch to the source code:

$ curl https://patch-diff.githubusercontent.com/raw/gnif/LookingGlass/pull/832.diff | patch -p1

Then build the client. Also install the systemd unit:

# cp contrib/looking-glass-client-suspend.service /etc/systemd/system/
# systemctl enable /etc/systemd/system/looking-glass-client-suspend.service

Then, suspend and resume the system, and see if the issue is resolved.

[gnif]

Just checking the status of things... Is this this PR still valid/in-progress etc?