Add support for exposing delegate observers.

[mswysocki]

Resolves #78

This change updated AutoDisposingSubscriber implement FlowableSubscriber instead of Subscriber. We wanted to have more consistency with how the rest of the Observers are handled in RxJava. This change remains backward compatible because FlowableSubscriber still extends Subscriber.

This also exposes all the different implementations of Observer to allow for introspection to the delegate Observer. This will be particularly useful for ReactiveX/RxJava#5590.

[CLAassistant]

All committers have signed the CLA.

[ZacSweers]

Looking good! From a high level I think there's a few changes we should make that are across the observers:

• Let's inline the {@link Observer} mentions in docs, it should read like a sentence since they are linkified inline. Make sure you link the correct observer as well (e.g. right now they all use Observer but there is a unique Observer for each type, like SingleObserver).
• Let's add a comment to the docs that explicitly call out that this API will change once the LambdaIntrospection stuff is out of @Experimental in RxJava (at which point we'll update it to return that interface instead and mark it nullable to return null upon non conforming types).
• Let's add @Experimental to all the methods to indicate their plans to change. Borrow the RxJava annotation.
• Let's make the atomic references in tests local to their specific unit tests rather than fields since they're only used in those methods.
• Use reference comparison for the delegate observer in tests, not isEqualTo (which checks equality and isn't what we want).

[ZacSweers]

Nit: would be good to include a tidbit of the explanation you put in the PR description in this commit message

[ZacSweers]

Nit: Did you mean to link the Observer here rather than inline?

I'd expect this to be like @return The delegate {@link Observer} that is used under the hood for introspection purposes.

[ZacSweers]

This should be a reference check, not equality

[ZacSweers]

since these are only used in one test, let's make them final local variables in those methods instead

[ZacSweers]

wat.gif

[mswysocki]

I believe this was from you trying to use my keyboard.

[mswysocki]

Let's inline the {@link Observer} mentions in docs, it should read like a sentence since they are linkified inline. Make sure you link the correct observer as well (e.g. right now they all use Observer but there is a unique Observer for each type, like SingleObserver).

e3dd21a

Let's add a comment to the docs that explicitly call out that this API will change once the LambdaIntrospection stuff is out of @experimental in RxJava (at which point we'll update it to return that interface instead and mark it nullable to return null upon non conforming types).

bda1040

Let's add @experimental to all the methods to indicate their plans to change. Borrow the RxJava annotation.

bda1040

Let's make the atomic references in tests local to their specific unit tests rather than fields since they're only used in those methods.

7270758

Use reference comparison for the delegate observer in tests, not isEqualTo (which checks equality and isn't what we want).

45e6c31

[ZacSweers]

Woo!