[2.0.0] API improvements and other fixes

There are some APIs that can be improved/simplified. This issue is to collect all the cases. This is also a good place to raise and discuss any proposals or concerns.

• flatMap - add default value for the maxConcurrency argument, remove flatMap variants without the maxConcurrency argument
• flatMap with resultSelector - reorder arguments in the following way: resultSelector, maxConcurrency, mapper
• observableInterval - put startDelayMillis after periodMillis and add default value startDelayMillis: Long = periodMillis, remove another observableInterval variant
• Observable.replay - add default for bufferSize argument, remove the variant without arguments
• Completable.asMaybe and Completable.asObservable - remove the generic parameter and make the return generic type Nothing
• doOnAfterSuccess - rename action argument to consumer
• remove all deprecated code
• repeat(count: Int = -1) - the argument name should be times, for consistency with retry and RxJava. The type should be Long, and the default value should be Long.MAX_VALUE.
• repeat with value 0 should return empty Observable, repeat with value 1 should subscribe only once, and so on. For consistency with RxJava.
• retry(times: Int) - the argument type should be Long, and the default value should be Long.MAX_VALUE.
• Observable.scan(getSeed, accumulate) and Observable.scan(accumulate), - the accumulate argument should be renamed to accumulator for consistency with RxJava.
• Observable.throttle - should accept a Scheduler for timings instead of using Clock implicitly, for better testing on the client side.
• Review all ExperimentalReaktiveApi, perhaps we can stabilise something.
• Add collect overload with collection supplier
• Convert all millis durations to the new Duration API, if it becomes stable
• Wait for Multiple Receivers to become stable and extract all subscribeXyz extensions from DisposableScope, and also T.scope(dispose: (T) -> Unit)
• Stabilize the Plugins API
• Remove the old memory model support, optimize for the new memory model
• All limit arguments in Observable.buffer operators should be of type Int

[arkivanov]

@plusmobileapps yes, we have this in the task list for v2. I will investigate and provide updates here.

[arkivanov]

@galdp Yes it is. threadLocal is useful for as long as the Kotlin/Native strict memory model is used. If you opt-in to the new relaxed memory model, then you can avoid using threadLocal. Also as a side note, it is not quite related to the version of coroutines.