A good portion of geometry handling code was written during the X11
times. The main difference between X11 and Wayland is that kwin doesn't
know where a window will exactly be after resize() or moveResize().

In order to handle Wayland specifics, every window has a bounding
geometry that is being manipulated by move(), resize(), and moveResize().
The frameGeometry(), the clientGeometry(), and the bufferGeometry() are
not manipulated by move(), resize(), and moveResize() directly. Almost
everything that manipulates geometry should use moveResizeGeometry().

This creates a problem though, since the clientGeometry() will be
updated only after the client provides a new buffer, kwin has absolutely
no idea what the client geometry for a given move resize geometry will
be.

Another side of the coin is that decoration updates are performed
asynchronously on wayland, meaning that you cannot use border properties
for anything related to geometry handling and you should avoid using
borderLeft(), borderTop(), borderRight(), and borderBottom() in general.

clientGeometry(), bufferGeometry(), and border*() are good only if you
want to forward an event or render something. They can't be used for
manipulating the geometry.

Unfortunately, AbstractClient::checkWorkspacePosition() needs both,
which is a bit of a problem. To add more oil to the fire, contents
of a decorated window can be snapped to a screen edge. This goes against
the nature of geometry updates on wayland, where we try to indicate
the bounds of the frame geometry and avoid using client and buffer
geometries.

In order to make geometry handling more correct on wayland, this change
removes the ability to snap the contents of a decorated window to a
screen edge. This allows to avoid using the client geometry in
checkWorkspacePosition(), which is a very important function that ensures
the window is inside the workspace.

There is nothing wrong with snapping the frame rather than its contents
and that's what kwin used to do. It was changed with the removal of
"Display borders on maximized windows" option, the relevant commit
didn't provide any reasoning behind the change.