[SPARK-9753] [SQL] TungstenAggregate should also accept InternalRow instead of just UnsafeRow

https://issues.apache.org/jira/browse/SPARK-9753

This PR makes TungstenAggregate to accept `InternalRow` instead of just `UnsafeRow`. Also, it adds an `getAggregationBufferFromUnsafeRow` method to `UnsafeFixedWidthAggregationMap`. It is useful when we already have grouping keys stored in `UnsafeRow`s. Finally, it wraps `InputStream` and `OutputStream` in `UnsafeRowSerializer` with `BufferedInputStream` and `BufferedOutputStream`, respectively.

Author: Yin Huai <yhuai@databricks.com>

Closes #8041 from yhuai/joinedRowForProjection and squashes the following commits:

7753e34 [Yin Huai] Use BufferedInputStream and BufferedOutputStream.
d68b74e [Yin Huai] Use joinedRow instead of UnsafeRowJoiner.
e93c009 [Yin Huai] Add getAggregationBufferFromUnsafeRow for cases that the given groupingKeyRow is already an UnsafeRow.