[SPARK-18961][SQL] Support `SHOW TABLE EXTENDED ... PARTITION` statement

## What changes were proposed in this pull request?

We should support the statement `SHOW TABLE EXTENDED LIKE 'table_identifier' PARTITION(partition_spec)`, just like that HIVE does.
When partition is specified, the `SHOW TABLE EXTENDED` command should output the information of the partitions instead of the tables.
Note that in this statement, we require exact matched partition spec. For example:
```
CREATE TABLE show_t1(a String, b Int) PARTITIONED BY (c String, d String);
ALTER TABLE show_t1 ADD PARTITION (c='Us', d=1) PARTITION (c='Us', d=22);

-- Output the extended information of Partition(c='Us', d=1)
SHOW TABLE EXTENDED LIKE 'show_t1' PARTITION(c='Us', d=1);
-- Throw an AnalysisException
SHOW TABLE EXTENDED LIKE 'show_t1' PARTITION(c='Us');
```

## How was this patch tested?
Add new test sqls in file `show-tables.sql`.
Add new test case in `DDLSuite`.

Author: jiangxingbo <jiangxb1987@gmail.com>

Closes #16373 from jiangxb1987/show-partition-extended.