Add visual indicator for shape points

Nobody has claimed this yet.

## Use case

Currently when using the polygon or free shape tool, there's no visual indicator for where the points are when drawing the shape. This isn't the best, because it can be hard to figure out which point was the first point, or even what were points at all with the free shape tool. For example, you can't tell which point in the screenshot below is the first point:
Of course, you'd actually be the one drawing the shape so you'd know, but it could still be hard to figure out with more complex shapes. You're also unable to tell the amount of area you can click in to close the shape.

## Suggested solution
A visual indicator at each point showing that it's a point. It could be something simple like a white dot with a black outline. The first point could also additionally be a different color (like yellow or something) to know it's the first point. These indicators are only a preview and disappear when the shape is actually closed.

### Possible drawbacks
I'm not sure how hard it would be to implement this.

### Possible alternatives
Since quite a few of the issues are created by not knowing the first point, it might just be easier to only have an indicator for that point. There might also be another way to know where points are, or at the very least where the first point is.

Start by locating the polygon and free shape tool entry points and the code that renders their in-progress previews. Check how points are collected and how the shape is closed. Done means visible indicators appear at each point, distinguish the first point when useful, and disappear once the shape is closed.

Written by the indexing model from the issue text.