Code cleanup for GlutenPlugin

### Description

Currently, the GlutenPlugin have some code issue.

1. It doesn't follow the Scala code style.
2. It could clean up some code by import the constants from `GlutenConfig`.
3. Removes the hard code by references `SQLConf`. Such as: replaces `"spark.sql.parquet.enableVectorizedReader"` with `SQLConf.PARQUET_VECTORIZED_READER_ENABLED.key`.
4. We can simplify some code.