[SPARK-3873][CORE] Import ordering fixes.

core/src/main/scala/org/apache/spark/ContextCleaner.scala

...in/scala/org/apache/spark/ExecutorAllocationManager.scala

core/src/main/scala/org/apache/spark/HeartbeatReceiver.scala

core/src/main/scala/org/apache/spark/HttpServer.scala

core/src/main/scala/org/apache/spark/MapOutputTracker.scala

core/src/main/scala/org/apache/spark/Partitioner.scala

core/src/main/scala/org/apache/spark/SparkConf.scala

core/src/main/scala/org/apache/spark/SparkContext.scala

core/src/main/scala/org/apache/spark/SparkEnv.scala

core/src/main/scala/org/apache/spark/SparkHadoopWriter.scala

...rc/main/scala/org/apache/spark/api/java/JavaPairRDD.scala

...rc/main/scala/org/apache/spark/api/java/JavaRDDLike.scala

...in/scala/org/apache/spark/api/java/JavaSparkContext.scala

...la/org/apache/spark/api/java/JavaSparkStatusTracker.scala

.../src/main/scala/org/apache/spark/api/java/JavaUtils.scala

...rc/main/scala/org/apache/spark/api/python/PythonRDD.scala

.../main/scala/org/apache/spark/api/python/PythonUtils.scala

...ala/org/apache/spark/api/python/PythonWorkerFactory.scala

...rc/main/scala/org/apache/spark/api/python/SerDeUtil.scala

.../spark/api/python/WriteInputFormatTestDataGenerator.scala