1.9.0-RC.2

• Advanced the deprecation levels for BroadcastChannel-based API (#4197).
• Advanced the deprecation levels for the old kotlinx-coroutines-test API (#4198).
• Promoted CoroutineStart.ATOMIC from ExperimentalCoroutinesApi to DelicateCoroutinesApi (#4169).
• Reworked the documentation for CoroutineStart and Channel-based API (#4147, #4148, #4167). Thanks, @globsterg!
• Forbid casting a Mutex to Semaphore (#4176).
• Deprecated Job.cancelFutureOnCompletion (#4156).
• Worked around a stack overflow that may occur when calling asDeferred on a Future many times (#4156).
• Fixed a bug that disallowed setting a custom probeCoroutineResumed when starting coroutines with UNDISPATCHED (#4162).
• No longer initialize Dispatchers.IO on the JVM when other standard dispatchers are accessed (#4166). Thanks, @metalhead8816!
• Small tweaks, fixes, and documentation improvements.