Layer control instead of drop-down

I think it might be good to introduce a proper "layer control". This is what it's called in GIS but the concept is the same here. Let me explain:

Currently you can toggle between:

• "points"
• "density"

However, this is misleading as "density" also displays points.
Also, if you select a text column, labels will show always and you cannot turn them off.

Proposal:

Instead of the dropdown, what GIS uses for this is a simple multiselect (ignore Canada Base section):

Image source: https://github.com/drecchia/maplibre-layer-control

This would solve a few problems:

• the naming would be fixed, as the density setting would then only control density and not points
• users could hide the points in density view
• I'd propose an additional option "labels", where users can turn them on or off and - as we already discussed in https://github.com/apple/embedding-atlas/issues/14 - potentially add a slider here to set the label density on various zoom levels.

As a side note: you could also include the base layer in this control, i.e. the black/white background plane and add a simple color picker if users prefer a differently colored background. But this might be out of scope for you.

Start by locating the current points/density dropdown and the label-rendering controls described in the issue; review the related discussion in issue 14. Done should mean a layer control can independently toggle points, density, and labels, while the optional base-layer and label-density ideas are confirmed as in or out of scope.