Support ObservableInput consistently as the return type for selector fns (like delayWhen)

[jollytoad]

Some operators such as bufferWhen, windowWhen, audit allow their selector fn to return an ObservableInput which really helps with interop with native JS features, such as Promises, Iterables/AsyncIterables etc.

But the delayWhen delayDurationSelector fn must return an Observable, it would really help if this was also ObservableInput. I'm not sure if this is intentional (I don't understand why it would be), or an oversight. I'm not sure if this is the case elsewhere, but it would certainly help if it was consistent across all selector fns.

[benlesh]

Core Team: delayWhen should definitely be fixed. We'll need to look to see what other operators have this issue.

[jakovljevic-mladen]

Created issue for delayWhen: #7046

[jakovljevic-mladen]

So far, I've found that:

• buffer's closingNotifier,
• distinct's flushes,
• repeatWhen's notifier,
• sample's notifier,
• retryWhen's notifier,
• sequenceEqual's compareTo,
• ShareConfig's resetOnError, resetOnComplete and resetOnRefCountZero,
• skipUntil's notifier and
• window's windowBoundaries

could potentially extend Observable to ObservableInput. @benlesh, could you please review the list and let me know which of these operators should be updated?

[benlesh]

Yes, these should all be ObservableInput.