reactor/reactor-core v3.3.4.RELEASE on GitHub

reactor-core 3.3.4.RELEASE is part of Dysprosium-SR6 Release Train.

⚠️ Update considerations and deprecations

Introduce and use VirtualTimeScheduler#getOrSet(boolean) (#2060, #2017)
- VirtualTimeScheduler did not run scheduled tasks since 3.3.3.RELEASE
retryWhen(Function), all retryBackoff and retry(Predicate)/retry(long, Predicate) are now deprecated, to be replaced by the more generic retryWhen(Retry) (see RetrySpec and RetryBackoffSpec for configurable builders that cover these methods and more)

Refactor of retryWhen to switch to a Spec/Builder model (#1979, #1978, #1905, #2063, #2052, #2064, #2079)
- The new model is slated to replace retryWhen(Function) and retryBackoff as well as some retry variants in 3.4.0
- The API is build around the Retry abstract class, with two builders (or Spec) to fluently configure the retries
- This allows us to introduce additional new features:
  - all variants support a filter for errors to be retried
  - we now have sync and async retry callbacks when retry triggers
  - we can customize the exception to be thrown when max attempts is reached and we
  - transient bursts of errors can be handled separately, resetting eg. the backoff to its minimum provided at least one onNext comes in between errors
In repeatWhen and retryWhen, when a Context is emitted, we now merge it with the current instead of replacing it (#2056)

Mono.toFuture() now avoids invoking cancel after completion (#2070)
Various fixes in switchOnFirst (#2019, #2068)
- inner stream cancellation is better taken into account
- some race conditions have been fixed
- race conditions are tested
- cancellation signal of the whole sequence is correctly forwarded to the inner flux
the new API VirtualTimeScheduler#getOrSet(boolean) fixes virtual time in the StepVerifier (#2060, #2017)