Migrate Continuation to kotlin (#47537)

Summary:
Pull Request resolved: #47537

Migrate Continuation interface to kotlin

changelog: [internal] internal

Reviewed By: javache

Differential Revision: D65738326

fbshipit-source-id: 1a119f6d349101951dc528583f3dbaf5441da91e

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/runtime/internal/bolts/Continuation.java → packages/react-native/ReactAndroid/src/main/java/com/facebook/react/runtime/internal/bolts/Continuation.kt

@@ -5,20 +5,16 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-package com.facebook.react.runtime.internal.bolts;
-
-import androidx.annotation.NonNull;
-import androidx.annotation.Nullable;
+package com.facebook.react.runtime.internal.bolts
 
 /**
  * A function to be called after a task completes.
  *
  * <p>If you wish to have the Task from a Continuation that does not return a Task be cancelled then
- * throw a {@link java.util.concurrent.CancellationException} from the Continuation.
+ * throw a [java.util.concurrent.CancellationException] from the Continuation.
  *
  * @see Task
  */
 public interface Continuation<TTaskResult, TContinuationResult> {
-  @Nullable
-  TContinuationResult then(@NonNull Task<TTaskResult> task) throws Exception;
+  @Throws(Exception::class) public fun then(task: Task<TTaskResult>): TContinuationResult?
 }