Function llToTilePx

llToTilePx(
    ll: VectorPoint,
    tile: [zoom: number, x: number, y: number],
    tileSize?: number,
): VectorPoint
given a lon-lat and tile, find the offset in pixels
Parameters
- ll: VectorPoint
  the lon-lat
- tile: [zoom: number, x: number, y: number]
  the tile
- tileSize: number = 512
  in pixels
Returns VectorPoint
- the tile x-y