@Nonnull
	public static <K, V, C extends Collection<V>> MultiMap<K, V, C> from(Map<K, C> map, Supplier<? extends C> collectionSupplier) {
		return new MultiMap<>(map, collectionSupplier);
	}
Creates a multi-map.

@param map
		Backing map.
@param collectionSupplier
		Supplier for collections of values.
@param <K>
		Key type.
@param <V>
		Value type.
@param <C>
		Collection type.

@return New multi-map.
recaf-core/src/main/java/software/coley/recaf/util/MultiMap.java