maplibre/maplibre-gl-js ? reverse-engineered prompt

I want to build a JavaScript library for showing really beautiful, fast, and interactive maps on a website. The performance should be great, so it feels smooth when users pan, zoom, and tilt the view.

It needs to be great for data visualization. I want to be able to do things like show population density with a heatmap layer, display buildings in 3D for cityscapes, and render realistic 3D terrain. The visual style of the map should be completely customizable.

This should be built as a TypeScript library that can be easily dropped into any web page. It should be easy to get started, maybe with just a simple script tag and a div. Please also create a simple demo page that shows how to load a basic map centered on a specific city and demonstrates some of these features.