Minor Description
This is a pre-requisite of https://github.com/apache/spark/pull/32476, in discussion of https://github.com/apache/spark/pull/32476#issuecomment-836469779 . This is to refactor sort merge join code-gen to depend on streamed/buffered terminology, which makes the code-gen agnostic to different join types and can be extended to support other join types than inner join.
