This removes the final dependency on CoreVideo, using a display link to
get the refresh rate of monitors where Core Graphics report a refresh
rate of zero.  Instead we now query the I/O registry directly, similarly
to what the display link does at creation.

Thanks to @OneSadCookie for pointers to this solution.

(cherry picked from commit 4ec7daf3e92440efab8dac7c1f4c60707d990ed0)