Parser: add support for show, create, etc.. statement

[xuanyuan300]

Development Task

Add support for show, create, etc.. statement.

• [ ] create
• [x] show

[xuanyuan300]

So far, has supported as follows:

• ShowDatabasesStmt
• ShowTablesStmt
• ShowColumnsStmt
• ShowCreateTable

Also, some frequently used show statements should be supported， as follows:

• [x] show_create_trigger_stmt
• [x] show_create_user_stmt
• [x] show_create_view_stmt
• [x] show_engines_stmt
• [x] show_grants_stmt
• [x] show_keys_stmt
• [x] show_master_status_stmt
• [x] show_plugins_stmt
• [x] show_privileges_stmt
• [x] show_processlist_stmt
• [x] show_replica_status_stmt
• [x] show_replicas_stmt
• [x] show_status_stmt
• [x] show_triggers_stmt
• [x] show_variables_stmt

May be added in the future.

[wbtlb]

create stmt develop task

• [x] create
• [x] create_index_stmt
• [ ] create_resource_group_stmt
• [ ] create_role_stmt
• [ ] create_srs_stmt
• [ ] create_table_stmt