LTN tool, possible improvements to displaying turn-restrictions

Some ideas for improving the display of turn restrictions within the LTN tool:

- [ ] **Displaying cases where there is more than one turn restriction centred on the same node.** Currently if there are turn signs which overlap, only the last-drawn sign is visible. (Here is an example https://www.openstreetmap.org/node/11134462). This means that some turn restrictions are not visible to the user, which is potentially confusing.

- [x] **Mouse-over feature to highlight relevant road segments.** An optional extra feature (and a possible partial solution to the overlapping sign problem above) would be nice to have a mouse-over feature. When you move your mouse over the turn-restriction sign, it highlights the relevant road segments.

- [ ] **Scale by road width or fixed size?** For now I’ve stuck with the logic of adjusting the size of the icons to match the width of the road. In some cases this results in icons which are very small. This is inconsistent with the modal filters icons, which are fixed size. Would it be worth trying setting the turn restriction to a fixed size? Say 50% of the size of the modal filters?

(This issues where previously mentioned here https://github.com/a-b-street/abstreet/pull/1090#issuecomment-1604978123)