Replace mapbox-gl with maplibre-gl on the frontend

[spwoodcock]

Is your feature request related to a problem? Please describe.

• Currently we use [email protected], the final version before they switched from BSD3 to their proprietary license. This version is 5yrs out of date by now.
• We also use a few mapbox plugins: draw, geocoder, language (plus an ancient plugin mapbox-gl-draw-rectangle-mode that is probably no longer needed).

Describe the solution you'd like

A migration plan from mapbox --> maplibre, taking us into the future:

• Replace mapbox-gl with maplibre-gl. Hopefully this part is easy and it's mostly a drop-in replacement.
• Replace @mapbox/mapbox-gl-geocoder with @maplibre/maplibre-gl-geocoder.
• @mapbox/mapbox-gl-draw is still open and probably fine to use, but we could consider a migration to TerraDraw if needed.
• Uncertain about @mapbox/mapbox-gl-language for now - I feel this is probably simply built into the maplibre style spec by now - but could potentially keep using this too if needed as it's open BSD-3 license.

Describe alternatives you've considered

• There aren't other great alternatives with a clear migration pathway.
• As our map usage is pretty limited, we could consider leaflet, but would lose the WebGL performance gains.

Additional context

• Requirement for approval as a Digital Public Good.