Replace leaflet-mapbox-vector-tile with protomaps-leaflet

[t83714]

Replace leaflet-mapbox-vector-tile with protomaps-leaflet

We use leaflet-mapbox-vector-tile to draw region boundaries in the region filter panel UI on a leaflet map.

It would be good to replace it with the newer protomaps-leaflet library:

https://github.com/protomaps/protomaps-leaflet

Example usage of protomaps can be found from: https://github.com/protomaps/protomaps-leaflet/tree/main/examples

[t83714]

Add more comments from @steve9164

This is the current implementation using protomaps. It doesn't import protomaps-leaflet, but heavily borrows from it to write our renderer. To add a new method of tiled rendering to Terria, we add a custom Cesium ImageryProvider class (implementing the method requestImage(x: number, y: number, level: number) most importantly, and a few others for feature picking etc.). Leaflet plugins match fairly closely to the functionality that we need from a custom Cesium ImageryProvider class, but the interface is different enough that it's annoying (and less performant) to implement the new ImageryProvider by wrapping the Leaflet plugin. Because of this, we usually use the Leaflet plugin as a guide to write our code