ImageOverlayPlugins: Add MVT Support

[gkjohnson]

Based on #1469

Add support for MVT tiles as an image overlay with the goal of supporting MVT and PMTiles formats. MVT is assumed to be served in an XYZ slippy-maps style format.

Future

• TerrainRGB (somehow enable PMTiles to be a data source instead of fetch?)
• Hovering, mouse effect
• Consider performance improvements for drawing
  • "bake" paths into a Path2D, preparse all features
  • redraw only visible tiles
  • webworker-based drawing
  • parsed to 3d assets, drawn (ala MapLibre, Overture Maps, Mapbox)
  • skip redrawing tiles that do not include changed styles
• Scale lines, points based on projected world size
• Adjust texture resolution based on world size (possibly fixes above)
• Register MVT as a "texture type" or "drawable type" and PMTiles as a "fetch protocol" of sorts.
• Mark associated tiled formats in Plugins: Add support for other tiled formats #943

Style approach

styles: {
  rules: [
    { layer: 'water',    type: 'fill', paint: { 'fill-color': '#a0c8f0' } },
    { layer: 'building', type: 'fill', paint: { 'fill-color': '#e0e0e0', 'fill-opacity': 0.8 } },
    { layer: 'road',     type: 'line', paint: (f, l, z) => ({ 'line-width': z > 10 ? 2 : 1, 'line-color': '#888' }) },
    { type: 'fill',   paint: { 'fill-color': '#ffffff', 'fill-opacity': 0.3 } }, // fallback fill
    { type: 'line',   paint: { 'line-color': '#ffffff', 'line-width': 1 } },     // fallback line
    { type: 'circle', paint: { 'circle-color': '#ffffff', 'circle-radius': 3 } } // fallback circle
  ]
}

--

Triangulated geometry for flat or ellipsoidal surfaces will remain for future work since they are not applicable to overlays.

Vectorized shape notes

• Vectorized shapes can be triangulated with earcut
• If projected onto a sphere, the shape can be cut into a grid and projected
• Edges / points are mitered and scaled to screenspace in the vertex shader with offsets
• Once supported we could redraw these textures every frame and scale draped features, lines, etc