Rely on MProducerSupport.active for Flux (#3423)

* Rely on `MProducerSupport.active` for `Flux`

* Fix `MessageProducerSupport` to extract an `active` flag and set it before
`isRunning` - the `Flux` subscription relies on the `takeWhile()`
where in case of `autoStartup = false` we will never start consume because
it is set to `true` already after `doStart()`
* Refactor all the `MessageProducerSupport` implementation with similar
`active` state to use already one from the super class

**Cherry-pick to 5.3.x**

* * Remove `MessageProducerSupport.setActive()`
to not let to mutate it from the implementations
* Set `active` to `false` in the `destroy()`
* Clean up and fix typos in the affected `JmsMessageDrivenEndpoint`

* * Pull `active` flag down to the `AbstractEndpoint`
* Set `active = true` in the `start()` before calling `doStart()`
* Do same for `active = false` in the `stop()`
* Clean up `AbstractEndpoint` impls to not call `doStart/doStop` for nothing
* Refactor endpoints to rely on the `active` state from the `AbstractEndpoint`
not their own

spring-integration-core/src/test/java/org/springframework/integration/endpoint/ReactiveMessageProducerTests.java

@@ -16,7 +16,7 @@
 
 package org.springframework.integration.endpoint;
 
-import static org.assertj.core.api.Assertions.assertThat;
+import java.time.Duration;
 
 import org.junit.jupiter.api.Test;
 
@@ -50,17 +50,18 @@ public class ReactiveMessageProducerTests {
 
 	@Test
 	public void test() {
-		assertThat(this.producer.isRunning()).isTrue();
+		StepVerifier stepVerifier =
+				StepVerifier.create(
+						Flux.from(this.fluxMessageChannel)
+								.map(Message::getPayload)
+								.cast(String.class))
+						.expectNext("test1", "test2")
+						.thenCancel()
+						.verifyLater();
 
-		StepVerifier.create(
-				Flux.from(this.fluxMessageChannel)
-						.map(Message::getPayload)
-						.cast(String.class))
-				.expectNext("test1", "test2")
-				.thenCancel()
-				.verify();
+		this.producer.start();
 
-		assertThat(this.producer.isRunning()).isFalse();
+		stepVerifier.verify(Duration.ofSeconds(10));
 	}
 
 	@Configuration
@@ -79,10 +80,12 @@ public class ReactiveMessageProducerTests {
 
 						@Override
 						protected void doStart() {
+							super.doStart();
 							subscribeToPublisher(Flux.just("test1", "test2").map(GenericMessage::new));
 						}
 
 					};
+			producer.setAutoStartup(false);
 			producer.setOutputChannel(fluxMessageChannel());
 			return producer;
 		}