Fixes BUG: 403071
Please don't randomly turn methods into slots. There's a fair chance of future breaking if somebody checks for the usage of the slot and notices it's unused.
If you want to make a method invokable by scripts: use Q_INVOKABLE.
As far as I know, xdg-shell doesn't define maximized vertically or maximized horizontally states.
XdgShell protocol does not define it as a state, but ShellClient still accepts this as a regular window move.
I don't see it being an issue.