[SPARK-13544][SQL] Rewrite/Propagate Constraints for Aliases in Aggregate

#### What changes were proposed in this pull request?

After analysis by Analyzer, two operators could have alias. They are `Project` and `Aggregate`. So far, we only rewrite and propagate constraints if `Alias` is defined in `Project`. This PR is to resolve this issue in `Aggregate`.

#### How was this patch tested?

Added a test case for `Aggregate` in `ConstraintPropagationSuite`.

marmbrus sameeragarwal

Author: gatorsmile <gatorsmile@gmail.com>

Closes #11422 from gatorsmile/validConstraintsInUnaryNodes.