[SPARK-17272][SQL] Move subquery optimizer rules into its own file

## What changes were proposed in this pull request?
As part of breaking Optimizer.scala apart, this patch moves various subquery rules into a single file.

## How was this patch tested?
This should be covered by existing tests.

Author: Reynold Xin <rxin@databricks.com>

Closes #14844 from rxin/SPARK-17272.