[SPARK-47958][TESTS] Change LocalSchedulerBackend to notify scheduler…

… of executor on start

### What changes were proposed in this pull request?

Changing to call `reviveOffers` on start (after the local executor is set up) so that the task scheduler knows about it. This matches behavior in CoarseGrainedSchedulerBackend, which will call an equivalent method on executor registration.

### Why are the changes needed?

When using LocalSchedulerBackend, the task scheduler will not know about the executor until a task is run, which can lead to unexpected behavior in tests.

### Does this PR introduce _any_ user-facing change?
No.

### How was this patch tested?
Running existing tests.

### Was this patch authored or co-authored using generative AI tooling?
No.

Closes apache#46187 from davintjong-db/local-executor-fix.

Authored-by: Davin Tjong <davin.tjong@databricks.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>

core/src/main/scala/org/apache/spark/scheduler/local/LocalSchedulerBackend.scala

@@ -142,6 +142,7 @@ private[spark] class LocalSchedulerBackend(
         Map.empty)))
     launcherBackend.setAppId(appId)
     launcherBackend.setState(SparkAppHandle.State.RUNNING)
+    reviveOffers()
   }
 
   override def stop(): Unit = {