Promote the following experimental API to stable (#2971)

* transformWhile
* awaitClose and ProducerScope (for callbackFlow and channelFlow)
* merge
* runningFold, runningReduce, and scan

kotlinx-coroutines-core/common/src/channels/Produce.kt

@@ -6,14 +6,11 @@ package kotlinx.coroutines.channels
 
 import kotlinx.coroutines.*
 import kotlin.coroutines.*
+import kotlinx.coroutines.flow.*
 
 /**
- * Scope for the [produce][CoroutineScope.produce] coroutine builder.
- *
- * **Note: This is an experimental api.** Behavior of producers that work as children in a parent scope with respect
- *        to cancellation and error handling may change in the future.
+ * Scope for the [produce][CoroutineScope.produce], [callbackFlow] and [channelFlow] builders.
  */
-@ExperimentalCoroutinesApi
 public interface ProducerScope<in E> : CoroutineScope, SendChannel<E> {
     /**
      * A reference to the channel this coroutine [sends][send] elements to.
@@ -45,7 +42,6 @@ public interface ProducerScope<in E> : CoroutineScope, SendChannel<E> {
  * }
  * ```
  */
-@ExperimentalCoroutinesApi
 public suspend fun ProducerScope<*>.awaitClose(block: () -> Unit = {}) {
     check(kotlin.coroutines.coroutineContext[Job] === this) { "awaitClose() can only be invoked from the producer context" }
     try {

kotlinx-coroutines-core/common/src/flow/operators/Limit.kt

@@ -112,7 +112,6 @@ public fun <T> Flow<T>.takeWhile(predicate: suspend (T) -> Boolean): Flow<T> = f
  * }
  * ```
  */
-@ExperimentalCoroutinesApi
 public fun <T, R> Flow<T>.transformWhile(
     @BuilderInference transform: suspend FlowCollector<R>.(value: T) -> Boolean
 ): Flow<R> =

kotlinx-coroutines-core/common/src/flow/operators/Merge.kt

@@ -90,7 +90,6 @@ public fun <T> Flow<Flow<T>>.flattenConcat(): Flow<T> = flow {
  * Applications of [flowOn], [buffer], and [produceIn] _after_ this operator are fused with
  * its concurrent merging so that only one properly configured channel is used for execution of merging logic.
  */
-@ExperimentalCoroutinesApi
 public fun <T> Iterable<Flow<T>>.merge(): Flow<T> {
     /*
      * This is a fuseable implementation of the following operator:
@@ -114,7 +113,6 @@ public fun <T> Iterable<Flow<T>>.merge(): Flow<T> {
  * Applications of [flowOn], [buffer], and [produceIn] _after_ this operator are fused with
  * its concurrent merging so that only one properly configured channel is used for execution of merging logic.
  */
-@ExperimentalCoroutinesApi
 public fun <T> merge(vararg flows: Flow<T>): Flow<T> = flows.asIterable().merge()
 
 /**

kotlinx-coroutines-core/common/src/flow/operators/Transform.kt

@@ -85,7 +85,6 @@ public fun <T> Flow<T>.onEach(action: suspend (T) -> Unit): Flow<T> = transform
  *
  * This function is an alias to [runningFold] operator.
  */
-@ExperimentalCoroutinesApi
 public fun <T, R> Flow<T>.scan(initial: R, @BuilderInference operation: suspend (accumulator: R, value: T) -> R): Flow<R> = runningFold(initial, operation)
 
 /**
@@ -97,7 +96,6 @@ public fun <T, R> Flow<T>.scan(initial: R, @BuilderInference operation: suspend
  * ```
  * will produce `[], [1], [1, 2], [1, 2, 3]]`.
  */
-@ExperimentalCoroutinesApi
 public fun <T, R> Flow<T>.runningFold(initial: R, @BuilderInference operation: suspend (accumulator: R, value: T) -> R): Flow<R> = flow {
     var accumulator: R = initial
     emit(accumulator)
@@ -118,7 +116,6 @@ public fun <T, R> Flow<T>.runningFold(initial: R, @BuilderInference operation: s
  * ```
  * will produce `[1, 3, 6, 10]`
  */
-@ExperimentalCoroutinesApi
 public fun <T> Flow<T>.runningReduce(operation: suspend (accumulator: T, value: T) -> T): Flow<T> = flow {
     var accumulator: Any? = NULL
     collect { value ->

reactive/kotlinx-coroutines-reactor/src/ReactorContext.kt

@@ -4,7 +4,6 @@
 
 package kotlinx.coroutines.reactor
 
-import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlin.coroutines.*
 import kotlinx.coroutines.reactive.*
 import reactor.util.context.*