planner: introduce the logical Expand for rollup syntax

[AilinKid]

Feature Request

Is your feature request related to a problem? Please describe:

Rollup syntax means the underlying data should always be replicated for N+1 times (N is equal to the number of group by items list size), Otherwise, rewriting them as multi-statements concat with the UNION clause is necessary which is not planned from our side.

So from the AST transformation, Logical Expand is necessary; besides, we also need some logical meta generated by Expand operator to do the groupingFunc rewrite, and this step is also should be done in the Logical phase.

tidb> explain select count(a) from t group by a, b with rollup;
+--------------------------------------+----------+--------------+---------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| id                                   | estRows  | task         | access object | operator info                                                                                                                                                                                                                 |
+--------------------------------------+----------+--------------+---------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| TableReader_43                       | 8000.00  | root         |               | MppVersion: 1, data:ExchangeSender_42                                                                                                                                                                                         |
| └─ExchangeSender_42                  | 8000.00  | mpp[tiflash] |               | ExchangeType: PassThrough                                                                                                                                                                                                     |
|   └─Projection_37                    | 8000.00  | mpp[tiflash] |               | Column#7                                                                                                                                                                                                                      |
|     └─HashAgg_35                     | 8000.00  | mpp[tiflash] |               | group by:Column#4, Column#5, gid, funcs:count(test.t.a)->Column#7                                                                                                                                                             |
|       └─ExchangeReceiver_21          | 10000.00 | mpp[tiflash] |               |                                                                                                                                                                                                                               |
|         └─ExchangeSender_20          | 10000.00 | mpp[tiflash] |               | ExchangeType: HashPartition, Compression: FAST, Hash Cols: [name: Column#4, collate: binary], [name: Column#5, collate: binary], [name: gid, collate: binary]                                                                 |
|           └─Expand_19                | 10000.00 | mpp[tiflash] |               | level-projection:[test.t.a, <nil>->Column#4, <nil>->Column#5, 0->gid],[test.t.a, Column#4, <nil>->Column#5, 2->gid],[test.t.a, Column#4, Column#5, 6->gid]; schema: [Column: [test.t.a,Column#4,Column#5,gid] Unique key: []] |
|             └─Projection_15          | 10000.00 | mpp[tiflash] |               | test.t.a, test.t.a, test.t.b                                                                                                                                                                                                  |
|               └─TableFullScan_16     | 10000.00 | mpp[tiflash] | table:t       | keep order:false, stats:pseudo                                                                                                                                                                                                |
+--------------------------------------+----------+--------------+---------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
9 rows in set (0.00 sec)

Describe the feature you'd like:

introduce the logical Expand for rollup syntax

Describe alternatives you've considered:

Union statements rewriting (NOT considered now)

Teachability, Documentation, Adoption, Migration Strategy:

None