Merge adjacent `CompoundChunkOperator`s

[leiysky]

When building Pipeline, we will directly map the PhysicalPlan to the corresponding Processors.

It's possible to merge adjacent CompoundChunkOperators if there are adjacent Filter and EvalScalar.

In the following case, we can merge CompoundChunkOperator of EvalScalar and Filter:

mysql> explain select number+1 from numbers(10) where number < 5;
+----------------------------------------------------------------------+
| explain                                                              |
+----------------------------------------------------------------------+
| EvalScalar                                                           |
| ├── expressions: [+(numbers.number (#0), 1)]                         |
| └── Filter                                                           |
|     ├── filters: [<(numbers.number (#0), 5)]                         |
|     └── TableScan                                                    |
|         ├── table: default.system.numbers                            |
|         ├── read rows: 10                                            |
|         ├── read bytes: 80                                           |
|         ├── partitions total: 1                                      |
|         ├── partitions scanned: 1                                    |
|         └── push downs: [filters: [(number < 5)], limit: NONE]       |
+----------------------------------------------------------------------+
11 rows in set (0.18 sec)
Read 0 rows, 0.00 B in 0.045 sec., 0 rows/sec., 0.00 B/sec.