[optimizer] Add Column Pruning Rule

[yixinglu]

Plan fragment could be applied this rule:

-----+--------------------+--------------+----------------+--------------------------------------------------------------------------------------------
| 27 | Project            | 30           |                | outputVar: [                                                                              |
|    |                    |              |                |   {                                                                                       |
|    |                    |              |                |     "colNames": [                                                                         |
|    |                    |              |                |       "v2"                                                                                |
|    |                    |              |                |     ],                                                                                    |
|    |                    |              |                |     "type": "DATASET",                                                                    |
|    |                    |              |                |     "name": "__Project_27"                                                                |
|    |                    |              |                |   }                                                                                       |
|    |                    |              |                | ]                                                                                         |
|    |                    |              |                | inputVar: __Filter_26                                                                     |
|    |                    |              |                | columns: [                                                                                |
|    |                    |              |                |   "$v2"                                                                                   |
|    |                    |              |                | ]                                                                                         |
-----+--------------------+--------------+----------------+--------------------------------------------------------------------------------------------
| 30 | Filter             | 24           |                | outputVar: [                                                                              |
|    |                    |              |                |   {                                                                                       |
|    |                    |              |                |     "colNames": [                                                                         |
|    |                    |              |                |       "v",                                                                                |
|    |                    |              |                |       "e",                                                                                |
|    |                    |              |                |       "v2",                                                                               |
|    |                    |              |                |       "__COL_0"                                                                           |
|    |                    |              |                |     ],                                                                                    |
|    |                    |              |                |     "type": "DATASET",                                                                    |
|    |                    |              |                |     "name": "__Filter_26"                                                                 |
|    |                    |              |                |   }                                                                                       |
|    |                    |              |                | ]                                                                                         |
|    |                    |              |                | inputVar: __Project_24                                                                    |
|    |                    |              |                | condition: (($v2.age>30) AND !(hasSameEdgeInPath($-.__COL_0)))                            |
-----+--------------------+--------------+----------------+--------------------------------------------------------------------------------------------
| 24 | Project            | 23           |                | outputVar: [                                                                              |
|    |                    |              |                |   {                                                                                       |
|    |                    |              |                |     "colNames": [                                                                         |
|    |                    |              |                |       "v",                                                                                |
|    |                    |              |                |       "e",                                                                                |
|    |                    |              |                |       "v2",                                                                               |
|    |                    |              |                |       "__COL_0"                                                                           |
|    |                    |              |                |     ],                                                                                    |
|    |                    |              |                |     "type": "DATASET",                                                                    |
|    |                    |              |                |     "name": "__Project_24"                                                                |
|    |                    |              |                |   }                                                                                       |
|    |                    |              |                | ]                                                                                         |
|    |                    |              |                | inputVar: __InnerJoin_23                                                                  |
|    |                    |              |                | columns: [                                                                                |
|    |                    |              |                |   "startNode($-._path_0) AS v",                                                           |
|    |                    |              |                |   "relationships($-._path_0) AS e",                                                       |
|    |                    |              |                |   "startNode($-._path_1) AS v2",                                                          |
|    |                    |              |                |   "PathBuild[PathBuild[$-._path_0,$-._path_1]] AS __COL_0"                                |
|    |                    |              |                | ]                                                                                         |
-----+--------------------+--------------+----------------+--------------------------------------------------------------------------------------------

The result set needs not the variables e and v, we can prune the columns in optimization stage and avoid useless evaluation at runtime.