[SPARK-12850][SQL] Support Bucket Pruning (Predicate Pushdown for Bucketed Tables)

JIRA: https://issues.apache.org/jira/browse/SPARK-12850

This PR is to support bucket pruning when the predicates are `EqualTo`, `EqualNullSafe`, `IsNull`, `In`, and `InSet`.

Like HIVE, in this PR, the bucket pruning works when the bucketing key has one and only one column.

So far, I do not find a way to verify how many buckets are actually scanned. However, I did verify it when doing the debug. Could you provide a suggestion how to do it properly? Thank you! cloud-fan yhuai rxin marmbrus

BTW, we can add more cases to support complex predicate including `Or` and `And`. Please let me know if I should do it in this PR.

Maybe we also need to add test cases to verify if bucket pruning works well for each data type.

Author: gatorsmile <gatorsmile@gmail.com>

Closes #10942 from gatorsmile/pruningBuckets.