[SPARK-14161][SQL] Native Parsing for DDL Command Drop Database

### What changes were proposed in this pull request?
Based on the Hive DDL document https://cwiki.apache.org/confluence/display/Hive/LanguageManual+DDL

The syntax of DDL command for Drop Database is
```SQL
DROP (DATABASE|SCHEMA) [IF EXISTS] database_name [RESTRICT|CASCADE];
```
 - If `IF EXISTS` is not specified, the default behavior is to issue a warning message if `database_name` does't exist
 - `RESTRICT` is the default behavior.

This PR is to provide a native parsing support for `DROP DATABASE`.

#### How was this patch tested?

Added a test case `DDLCommandSuite`

Author: gatorsmile <gatorsmile@gmail.com>

Closes #11962 from gatorsmile/parseDropDatabase.