[SPARK-13661][SQL] avoid the copy in HashedRelation

## What changes were proposed in this pull request?

Avoid the copy in HashedRelation, since most of the HashedRelation are built with Array[Row], added the copy() for LeftSemiJoinHash. This could help to reduce the memory consumption for Broadcast join.

## How was this patch tested?

Existing tests.

Author: Davies Liu <davies@databricks.com>

Closes #11666 from davies/remove_copy.