This implements drawing the line endings for 2 point lines in non-PDF documents.
- Square, Diamond, OpenArrow, ClosedArrow, ROpenArrow, RClosedArrow, Butt, Slash
- for start and stop style (start can't be configured in GUI yet)
- filled or not (fill color can't be configured in GUI yet)
- with or without leader line
- shorten main segment
- Expose `LineAnnotPainter` so that it can be reused to generate preview icons
- What about multiline annotations?