Support different shapes for Points2D and Points3D

[roym899]

Is your feature request related to a problem? Please describe.
Currently Points2D and Points3D are visualized as circles and spheres, respectively. It would be nice to add more options such as cubes, flat points, etc. (see below for examples).

Describe the solution you'd like
Maybe this should be similar to the marker type of timeseries?

Describe alternatives you've considered
Currently you'd have to manually create a Mesh3D for what you want.

Additional context
The 2D equivalent for most plotting libraries would be the marker type that can be used in 2D scatter plots.

RViz supports visualizing point clouds with varying primitive types. This can then also be used to visualize a sparse voxel grid, when the points are evenly spaced.

For reference, RViz supports Points, Squares, Flat Squares, Spheres, Boxes, Tiles which look like the following:

[Wumpf]

I believe rather than adding shapes to Points2D and Points3D we'd rather have this be different archetypes that follow a similar structure. We're quite close to allowing changes of visualizer in the ui & blueprint.

Thus very related to:

• Support for more 2D and 3D primitives #1361
• Distinguish points, spheres and circles #2689

Not entirely sure yet. Always hard to tell where it's just a different marker or a whole new shape with its own (optional) configuration options.