window: make setQuickTileMode more sane
...by removing the keyboard flag, moving keyboard shortcut handling into a separate method and making the position to tile the window at explicit
This also means KWin doesn't do as many intermediary changes to window geometry on output hotplugs, which may work around some clients not always reacting to no-op changes.
There's more to be done, especially the interactions with maximize are rather annoying, but that can be done later.