[SPARK-12888] [SQL] [FOLLOW-UP] benchmark the new hash expression

Adds the benchmark results as comments.

The codegen version is slower than the interpreted version for `simple` case becasue of 3 reasons:

1. codegen version use a more complex hash algorithm than interpreted version, i.e. `Murmur3_x86_32.hashInt` vs [simple multiplication and addition](https://github.com/apache/spark/blob/master/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/rows.scala#L153).
2. codegen version will write the hash value to a row first and then read it out. I tried to create a `GenerateHasher` that can generate code to return hash value directly and got about 60% speed up for the `simple` case, does it worth?
3. the row in `simple` case only has one int field, so the runtime reflection may be removed because of branch prediction, which makes the interpreted version faster.

The `array` case is also slow for similar reasons, e.g. array elements are of same type, so interpreted version can probably get rid of runtime reflection by branch prediction.

Author: Wenchen Fan <wenchen@databricks.com>

Closes #10917 from cloud-fan/hash-benchmark.

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