A previous attempt was made in D1977[1] but it didn't work properly. The patch `0003-Hack-for-fullscreen-workaround.patch` only partly hid the issue and the issue has resurfaced since this patch was removed.
This commit actually enables Qt's workaround. The workaround adds a 1px border around the window. An additional hack is added to hide three of the borders, we can't hide all four borders since the bug will return. This currently leaves the bottom border visible as a compromise.
This workaround is not active when ANGLE is being used. If anyone is annoyed by the 1px border, they should consider switching to ANGLE.
[1]: https://phabricator.kde.org/D1977