Fix ABSTRACT_MEMBER_NOT_IMPLEMENTED compilation with newer Kotlin (#3805)

The compilation started failing after KT-59739

Author: nikitabobko

kotlinx-coroutines-core/common/src/flow/internal/SafeCollector.common.kt

@@ -18,6 +18,7 @@ internal expect class SafeCollector<T>(
     internal val collectContext: CoroutineContext
     internal val collectContextSize: Int
     public fun releaseIntercepted()
+    public override suspend fun emit(value: T)
 }
 
 @JvmName("checkContext") // For prettier stack traces

kotlinx-coroutines-core/js/src/flow/internal/SafeCollector.kt

@@ -17,7 +17,7 @@ internal actual class SafeCollector<T> actual constructor(
     internal actual val collectContextSize = collectContext.fold(0) { count, _ -> count + 1 }
     private var lastEmissionContext: CoroutineContext? = null
 
-    override suspend fun emit(value: T) {
+    actual override suspend fun emit(value: T) {
         val currentContext = currentCoroutineContext()
         currentContext.ensureActive()
         if (lastEmissionContext !== currentContext) {

kotlinx-coroutines-core/jvm/src/flow/internal/SafeCollector.kt

@@ -60,7 +60,7 @@ internal actual class SafeCollector<T> actual constructor(
      * then just cache an instance of the completion in order to avoid extra allocation on each emit,
      * making it effectively garbage-free on its hot-path.
      */
-    override suspend fun emit(value: T) {
+    actual override suspend fun emit(value: T) {
         return suspendCoroutineUninterceptedOrReturn sc@{ uCont ->
             try {
                 emit(uCont, value)

kotlinx-coroutines-core/native/src/flow/internal/SafeCollector.kt

@@ -17,7 +17,7 @@ internal actual class SafeCollector<T> actual constructor(
     internal actual val collectContextSize = collectContext.fold(0) { count, _ -> count + 1 }
     private var lastEmissionContext: CoroutineContext? = null
 
-    override suspend fun emit(value: T) {
+    actual override suspend fun emit(value: T) {
         val currentContext = currentCoroutineContext()
         currentContext.ensureActive()
         if (lastEmissionContext !== currentContext) {