Add support for `Arrows::width()`

**Is your feature request related to a problem? Please describe.**
Sometimes arrows can be hard to see (e.g. when they're along the X or Y axis) so it would be nice to be able to increase their width so they're more visible.

**Describe the solution you'd like**
Add `Arrows::width()`, which would work like `Line::width()` and similar.

**Describe alternatives you've considered**
`Arrows::highlight(true)` helps, but it would be nice to have more control than this offers.

**Additional context**