[SPARK-9420][SQL] Move expressions in sql/core package to catalyst.

[rxin]

Since catalyst package already depends on Spark core, we can move those expressions
into catalyst, and simplify function registry.

This is a followup of #7478.

[marmbrus]

LGTM

[rxin]

I also renamed spark__partition__id to spark_partition_id.

cc @JDrit

[JDrit]

The other function in the umbrella ticket was for input_file_name() in which @rxin has suggested to use a thread local variable in SqlNewHadoopRDD. That function could not be put in FunctionRegistry since it would need access to the SQL package right?

[rxin]

We can add the thread local variable in sql/core, and the expression itself in sql/catalyst? There is no build dependency for looking up thread local variables.

[SparkQA]

Test build #38770 has finished for PR 7735 at commit 2ffbdc3.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.