pdMouseInput: implement high-resolution cursor tracking

If my Google-fu is accurate, this is the first-ever publicly available
implementation of GetMouseMovePointsEx in vb6.  Neat!

A new setHighResolutionTrackingMode() function allows pdMouseInput users
to request high-resolution mouse movement tracking.  (The tracking mode
can be changed at any time, FYI.)

While this mode is active, pdMouseInput will reconstruct a full mouse
movement history, and raise every unique mouse coordinate in turn.  This
provides the highest possible mouse polling rate available via standard
Windows programs; for anything better, you'd have to manually parse the
raw input stream coming straight from the pointer device.

A word of warning is in order.  High-resolution tracking causes a *lot*
of MouseMove events to generate.  If the code within a MouseMove handler
is particularly time-consuming, this can lead to a nasty UX where
everything feels super laggy.  So use this feature with caution.

In the case of PD, I haven't actually activated the feature yet.  As a
failsafe, I think I may place functionality behind a preference, so that
users can disable it on extremely old PCs.  (Even with the preference,
PD will only activate the functionality for relevant controls, where
performance allows the feature to be awesome instead of annoying.)