=act let onReceive throw Throwable, #20231 (#20781)

* I also tried to change the lifecycle methods (e.g. postStop) but
  that would break source compatibility for code that called super.postStop

akka-actor/src/main/scala/akka/actor/UntypedActor.scala

@@ -98,7 +98,7 @@ abstract class UntypedActor extends Actor {
    * To be implemented by concrete UntypedActor, this defines the behavior of the
    * UntypedActor.
    */
-  @throws(classOf[Exception])
+  @throws(classOf[Throwable])
   def onReceive(message: Any): Unit
 
   /**

akka-persistence/src/main/scala/akka/persistence/PersistentActor.scala

@@ -291,7 +291,7 @@ abstract class UntypedPersistentActor extends UntypedActor with Eventsourced wit
    *
    * @see [[Recovery]]
    */
-  @throws(classOf[Exception])
+  @throws(classOf[Throwable])
   def onReceiveRecover(msg: Any): Unit
 
   /**
@@ -299,7 +299,7 @@ abstract class UntypedPersistentActor extends UntypedActor with Eventsourced wit
    * communication with other actors). On successful validation, one or more events are
    * derived from a command and these events are then persisted by calling `persist`.
    */
-  @throws(classOf[Exception])
+  @throws(classOf[Throwable])
   def onReceiveCommand(msg: Any): Unit
 }