2.x Why is FlowableEmitter.BackpressureMode and BackpressureStrategy not merged

[adipascu]

Why are the two enums not merged into one, they both serve the same purpose and both places where they are used should have the same features.

Also because
BackpressureStrategy.NONE does not exist, I currently can not use a BufferStrategy on an Observable

I don't think this code is simple easy

Observable.toFlowable(BackpressureStrategy.NONE)
.onBackpressureBuffer(10, Functions.EMPTY_ACTION, BackpressureOverflowStrategy.DROP_OLDEST)

[akarnokd]

If you can make it work, then PR welcome.

[akarnokd]

Closing via #4729