wayland: Interpret input panel's input shape as the window geometry

maliit creates a fullscreen overlay window which doesn't go along well
with out geometry abstractions. For example, raw frame geometry can't be
used to displace normal windows otherwise they will be pushed offscreen.

Some of the maliit quirks are leaked in the InputMethod class. After
extending the lifetime of the InputPanelV1Window, they can cause
problems.

In order to make code in InputMethod more intuitive and encapsulate
maliit quirks, this change makes InputPanelV1Window interpret the
bounding rectangle of the input shape as the window geometry. This
lets us get rid of the hack in inputGeometry() too.

The size checks in Mode::VirtualKeyboard case have been removed because
they should be irrelevant. When reposition() is called, the wl_surface
is mapped, so its size cannot be 0x0.