Summary:
This PR focuses on replacing some of the reinterpret_cast<DBImpl*> to static_cast_with_check<DBImpl, DB>.

Files impacted:

./db/db_impl/db_impl_compaction_flush.cc
./db/write_batch.cc
./utilities/blob_db/blob_db_impl.cc
./utilities/transactions/pessimistic_transaction_db.cc
./utilities/transactions/transaction_base.cc
./utilities/transactions/write_prepared_txn_db.cc
./utilities/transactions/write_unprepared_txn_db.cc
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5740

Differential Revision: D17055691

Pulled By: pdhandharia

fbshipit-source-id: 0f8034d1b32eade56e37d59c04b7bf236a81d8e8