Implement summary.isPartitioned()

[Smoren]

Returns true if all elements of given collection that satisfy the predicate appear before all elements that don't.

• Returns true for empty collection or for collection with single item.
• Default predicate if not provided is the boolean value of each data item.

function *isPartitioned<T>(...iterable: Iterable<T> | Iterator<T>, predicate?: (datum: T) => boolean): boolean

PHP implementation example

Needs to be implemented:

• summary.isPartitioned()
• summary.isPartitionedAsync()
• Stream.isPartitioned()
• AsyncStream.isPartitioned()