| index | The index of the key to move. |
| key | The key (with its new time) to insert. |
int The index of the keyframe after moving it.
Removes the keyframe at index and inserts key.
If a keyframe already exists at key.time the time of the old keyframe's position
/key[index].time/ will be used instead.
This is the desired behaviour for dragging keyframes in a curve editor.
Returns the index of the keyframe after moving it.