Refactor source interface to better accommodate non-tiled sources

[lucaswoj]

We currently shoehorn all source types into the VectorTileSource interface by abusing Tile objects. For example, ImageSource populates a single Tile with a number of ad-hoc properties. This architecture breaks and causes bugs like #3010.

There are several different types of sources in GL JS and each should have its own interface:

interface VectorTileSource {
    getVectorTileCoordURL(coord: TileCoord) => string;
    getVectorTile(url: string, callback: (error: Error, tile: VectorTile) => void) => void;
}

interface RasterTileSource {
    getRasterTileCoordURL(coord: TileCoord) => string;
    getRasterTile(url: string, callback: (error: Error, tile: ImageData) => void);
}

interface ImageSource {
    getImage(callback: (error: Error, image: ImageData) => void);
}

interface VideoSource {
    getVideo(callback: (error: Error, video: () => ImageData) => void);
}

Wiring up these interfaces to StyleLayers, SourceCache, etc will require some elbow grease and will be worth it. 💪 Note the elimination of Tile objects per #145.

Inspired by #3010 (comment)

Related to #2982 #281 #3010 #3123

[lucaswoj]

I just updated the interface proposals above to address the concerns of #3123 and the needs of #3051 🚀

[mourner]

@lucaswoj why does getVectorTile accept url but getRasterTile accept coord? I guess both should be either url or coord.

[lucaswoj]

@mourner Typo. Fixed above.

[1ec5]

This is also being tracked for the iOS and macOS SDKs in mapbox/mapbox-gl-native#6861, happening in mapbox/mapbox-gl-native#6940.

[anandthakker]

This refactor should also accommodate non-tiled vector sources.
Related issues:

• Add a synchronous version of GeoJSONSource#setData #2275
• Circle Layer disappears after certain zoom level #4954 (comment) / Large circle disappears when center is outside of visible map area #3431 (comment)