Import patch from upstream to fix key grabbing issues.

This replaces previous homegroown patch.

PR: 244290
Submitted by: aryeh.friedman@gmail.com
Tested by: Jethro Nederhof <jethro@jethron.id.au>
Obtained from: https://gitlab.xfce.org/xfce/libxfce4ui/-/merge_requests/27
MFH After: 1 week
MFH: 2021Q1