compositor: make surface_configure() a vfunc

This allows us to move the logic that calls shell->map() or
shell->configure() into shell while allowing it to be overriden for
surfaces that should not be handle by the shell, such as drag icons.

This patch adds a pointer function called configure to weston_surface,
moves the currsent surface_configure() code into shell and implements
a separate configure() for drag surfaces.
3 files changed