Add patch for Qt to support stylus button remapping

The user can remap the stylus buttons using tablet driver settings.
This information is available to the application via CSR_SYSBTNMAP
WinTab feature. We should fetch this information every time the
stylus gets into proximity, because the user can change these settings
on the fly.

See full patch review:
https://codereview.qt-project.org/#/c/258966/