Reuse FileFormat instead of DecodingFormat/EncodingFormat to ensure thread safety.

When testing table store I'm faced with the following warning messages:

org.apache.org.impl.MemoryManagerImpl [] - Owner thread expected Thread[Writer -> Local Committer (1/16)#0,5,Flink Task Threads], got Thread[pool-8-thread-1,5,Flink Task Threads]

This is because OrcBulkWriterFactory is not thread safe (it keeps WriterOptions as a class member and creates writers from the same WriterOptions object, which is not thread safe).

What we should do is to reuse FileFormat instead of DecodingFormat/EncodingFormat to ensure thread safety.