feat(tileset): Improve filter and spatial filter API for tilesets

[donmccurdy]

For tilesets, filters cannot be specified in source functions like vectorTilesetSource. Both filters and spatial filters need to be applied in a pre-pass on the tile data, before computing widget results. In #50 this was originally set up similarly to C4R, with three distinct steps for (1) loading tiles, (2) extracting tile features, and (3) computing results. For simpler usage, we'd like to hide step (2), and in most cases users can simply do this:

// (1)
widgetSource.loadTiles(tiles);

// (2)
const result = await widgetSource.getFormula({..., filters, spatialFilter});

For the less common cases where the storeGeometry or uniqueIdProperty options need to be specified, that can be done once, and doesnt need to be reconfigured when new tiles are loaded:

// (optional)
widgetSource.setTileExtractOptions({
  uniqueIdProperty: 'my_custom_id',
  storeGeometry: true
});