1-index angles to be consistent with DVD angles in mpv and with the
1-indexing in other applications like libbluray's example programs.
The three existing calls to bd_get_title_info all only access the
duration, the playlist, and the number of angles, which do not depend on
the passed angle, so they can keep being called with angle 0 for
simplicity.
Documentation taken from before
35e8b6c1e6.
Fixes#5012.
arch1t3cht
31bd176357