Testing line tool

Testcases:
- [x] Works when the viewport is zoomed/panned/tilted (#2559)
- [x] Works when the artboard has an offset (#2572)
- [x] Works when the artboard has a transform before it (#2572)
- [x] Shift constrains to 15 degrees from the viewport (test when the viewport is rotated by 5 degrees) (#2490)
- [x] Ctrl locks the angle when pressed (#2490)
- [x] Alt drags from centre (test when combined with shift as well) (#2490)
- [ ] After drawing, selected layers *only* can have their endpoints dragged.