Update Dispatchers.Main documentation (#3450)

Fixes #3381

Author: qwwdfsad

kotlinx-coroutines-core/common/src/Dispatchers.common.kt

@@ -27,16 +27,16 @@ public expect object Dispatchers {
      * Access to this property may throw an [IllegalStateException] if no main dispatchers are present in the classpath.
      *
      * Depending on platform and classpath, it can be mapped to different dispatchers:
-     * - On JS and Native it is equivalent to the [Default] dispatcher.
      * - On JVM it is either the Android main thread dispatcher, JavaFx or Swing EDT dispatcher. It is chosen by the
      *   [`ServiceLoader`](https://docs.oracle.com/javase/8/docs/api/java/util/ServiceLoader.html).
+     * - On JS it is equivalent to the [Default] dispatcher with [immediate][MainCoroutineDispatcher.immediate] support.
+     * - On Native Darwin-based targets, it is a dispatcher backed by Darwin's main queue.
+     * - On other Native targets, it is a single-threaded dispatcher backed by a standalone worker.
      *
      * In order to work with the `Main` dispatcher, the following artifact should be added to the project runtime dependencies:
      *  - `kotlinx-coroutines-android` — for Android Main thread dispatcher
      *  - `kotlinx-coroutines-javafx` — for JavaFx Application thread dispatcher
      *  - `kotlinx-coroutines-swing` — for Swing EDT dispatcher
-     *
-     * Implementation note: [MainCoroutineDispatcher.immediate] is not supported on the Native and JS platforms.
      */
     public val Main: MainCoroutineDispatcher