video: accept timecode of 119.88 (120/1.001) FPS

video: accept timecode of 119.88 (120/1.001) FPS

The drop-frame rules are specified in “SMPTE ST 12-3:2016” and are
consistent with the traditional ones:

“

To minimize fractional time deviation from real time, the first two
super-frame numbers (00 and 01) shall be omitted from the count at the
start of each minute except minutes 00, 10, 20, 30, 40, and 50. Thus the
first eight frame numbers (0 through 7) are omitted from the count at
the start of each minute except minutes 00, 10, 20, 30, 40, and 50.
”

Where “super-frame” is a group of 4 frames for 120 FPS.

Fixes #2797

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5061>