Improve overlapping subtitle UI
It is useful that we can overlap subtitles (translating speech while some text is shown, or simulating rolling subtitles, for example), but as it is now, the subtitles can hide other subtitles. Maybe reducing a subtitle to half size when they overlap and allow for at least 2? I was remembering some sort of overlap like this in the audio tracks, but was trying it now and can't get it to work. Maybe it was during same track clip mixing development? Can't really recall...