vo: different hack for VOs which need to mangle mouse input

Follow up on commit 760548da. Mouse handling is a bit confusing, because
there are at least 3 coordinate systems associated with it, and it
should be cleaned up. But that is hard, so just apply a hack which gets
the currently-annoying issue (VO backends needing access to the VO) out
of the way.
vo: remove vo_mouse_movement() wrapper

So that VO backends don't have to access the VO just for that.
input: be stricter about rejecting mouse input with --no-input-cursor

Apparently this switch means all mouse input should be strictly
rejected. Some VO backends (such as X11) explicitly disable all mouse
events if this option is set, but others don't. So check them in
input.c, which increases consistency.