[SPARK-3731] [PySpark] fix memory leak in PythonRDD

The parent.getOrCompute() of PythonRDD is executed in a separated thread, it should release the memory reserved for shuffle and unrolling finally.

Author: Davies Liu <davies.liu@gmail.com>

Closes #2668 from davies/leak and squashes the following commits:

ae98be2 [Davies Liu] fix memory leak in PythonRDD

core/src/main/scala/org/apache/spark/api/python/PythonRDD.scala

@@ -247,6 +247,11 @@ private[spark] class PythonRDD(
           // will kill the whole executor (see org.apache.spark.executor.Executor).
           _exception = e
           worker.shutdownOutput()
+      } finally {
+        // Release memory used by this thread for shuffles
+        env.shuffleMemoryManager.releaseMemoryForThisThread()
+        // Release memory used by this thread for unrolling blocks
+        env.blockManager.memoryStore.releaseUnrollMemoryForThisThread()
       }
     }
   }