## What changes were proposed in this pull request?
Refactor `UnsafeProjectionBenchmark` to use main method.
Generate benchmark result:
```
SPARK_GENERATE_BENCHMARK_FILES=1 build/sbt "catalyst/test:runMain org.apache.spark.sql.UnsafeProjectionBenchmark"
```
## How was this patch tested?
manual test
Closes#22493 from yucai/SPARK-25485.
Lead-authored-by: yucai <yyu1@ebay.com>
Co-authored-by: Yucai Yu <yucai.yu@foxmail.com>
Co-authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>
