pdInputMouse: enable auto-drop of severely delayed messages

With this commit, I have also enabled high-resolution cursor tracking by
default.  Combined with auto-dropping of delayed messages, PD's UI
responsiveness is now many many times better IMO.

In a nutshell, pdInputMouse will now compare message times against the
current system time (for MouseMove events only!).  If an event is
delayed beyond 100 ms, it will not be reported to the caller.

MouseDown/Up events are still reported normally, so move events will
*always* be synchronized to the coordinate where the mouse was pressed
and released.

The new auto-drop solution is much better than using a user preference
to control high-resolution mouse behavior, because now pdInputMouse will
basically make the best available use of hardware.  If a particular
action (say, panning an enormous image, or using a slider on a
long-running tool preview) takes a long time, the message queue will now
be handled as closely as it can to a sub-100 ms delay.  On old PCs where
even stock WM_MOUSEMOVE messages become delayed, this means much better
responsiveness than old versions of PD.  And on high-end PCs where we
can happily process every possible mouse event, the UX should now be
buttery smooth on anything that uses pdInputMouse (e.g. all on-canvas
tools and custom-built UCs).

This behavior may need to be toggled when painting, so I have still made
override functions available for potential future use.  Note that the
delay threshold is also user-settable, so if 100 ms is too large (or too
small) for a given task, it's easy to set a new threshold via
setAutoDropDelayThreshold().