groupChunkSetsByCount = chunkSets => {
						/** @type {Map<number, Array<Set<Chunk>>>} */
						const chunkSetsByCount = new Map();
						for (const chunksSet of chunkSets) {
							const count = chunksSet.size;
							let array = chunkSetsByCount.get(count);
							if (array === undefined) {
								array = [];
								chunkSetsByCount.set(count, array);
							}
							array.push(chunksSet);
						}
						return chunkSetsByCount;
					}
@param {IterableIterator<Set<Chunk>>} chunkSets set of sets of chunks
@returns {Map<number, Array<Set<Chunk>>>} map of sets of chunks by count