function getCacheKey(source, sourceKey, z, x, y) {
  return `${getUid(source)},${sourceKey},${getKeyZXY(z, x, y)}`;
}
@param {import("../../source/Tile.js").default} source The tile source.
@param {string} sourceKey The source key.
@param {number} z The tile z level.
@param {number} x The tile x level.
@param {number} y The tile y level.
@return {string} The cache key.