## What changes were proposed in this pull request?
Refactor ExternalAppendOnlyUnsafeRowArrayBenchmark to use main method.
## How was this patch tested?
Manually tested and regenerated results.
Please note that `spark.memory.debugFill` setting has a huge impact on this benchmark. Since it is set to true by default when running the benchmark from SBT, we need to disable it:
```
SPARK_GENERATE_BENCHMARK_FILES=1 build/sbt ";project sql;set javaOptions in Test += \"-Dspark.memory.debugFill=false\";test:runMain org.apache.spark.sql.execution.ExternalAppendOnlyUnsafeRowArrayBenchmark"
```
Closes#22617 from peter-toth/SPARK-25484.
Lead-authored-by: Peter Toth <peter.toth@gmail.com>
Co-authored-by: Peter Toth <ptoth@hortonworks.com>
Co-authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>
