[GLUTEN-12413][VL] Enable ReusedExchange by normalizing Generate pre-project expressions as Alias

[jiangjiangtian]

Fix #12413.
After the fix, the plan is:

== Physical Plan ==
VeloxColumnarToRow
+- ^(6) BroadcastHashJoinExecTransformer [emp_id#19], [emp_id#27], Inner, BuildRight, false
   :- ^(6) HashAggregateTransformer(keys=[emp_id#19, emp_name#20], functions=[count(1)], isStreamingAgg=false)
   :  +- ^(6) InputIteratorTransformer[emp_id#19, emp_name#20, count#42L]
   :     +- ColumnarExchange hashpartitioning(emp_id#19, emp_name#20, 2000), ENSURE_REQUIREMENTS, [emp_id#19, emp_name#20, count#42L], [plan_id=2005], [shuffle_writer_type=hash], [OUTPUT] List(emp_id:IntegerType, emp_name:StringType, count:LongType)
   :        +- VeloxResizeBatches 1024, 2147483647, 10485760
   :           +- ^(2) ProjectExecTransformer [hash(emp_id#19, emp_name#20, 42) AS hash_partition_key#70, emp_id#19, emp_name#20, count#42L]
   :              +- ^(2) FlushableHashAggregateTransformer(keys=[emp_id#19, emp_name#20], functions=[partial_count(1)], isStreamingAgg=false)
   :                 +- ^(2) ProjectExecTransformer [emp_id#19, emp_name#20]
   :                    +- ^(2) HashAggregateTransformer(keys=[emp_id#19, emp_name#20, dept_names#21, sale#22], functions=[], isStreamingAgg=false)
   :                       +- ^(2) InputIteratorTransformer[emp_id#19, emp_name#20, dept_names#21, sale#22]
   :                          +- ColumnarExchange hashpartitioning(emp_id#19, emp_name#20, dept_names#21, sale#22, 2000), ENSURE_REQUIREMENTS, [emp_id#19, emp_name#20, dept_names#21, sale#22], [plan_id=1996], [shuffle_writer_type=hash], [OUTPUT] List(emp_id:IntegerType, emp_name:StringType, dept_names:StringType, sale:IntegerType)
   :                             +- VeloxResizeBatches 1024, 2147483647, 10485760
   :                                +- ^(1) ProjectExecTransformer [hash(emp_id#19, emp_name#20, dept_names#21, sale#22, 42) AS hash_partition_key#69, emp_id#19, emp_name#20, dept_names#21, sale#22]
   :                                   +- ^(1) FlushableHashAggregateTransformer(keys=[emp_id#19, emp_name#20, dept_names#21, sale#22], functions=[], isStreamingAgg=false)
   :                                      +- ^(1) ProjectExecTransformer [emp_id#19, emp_name#20, dept_names#21, sale#22]
   :                                         +- ^(1) GenerateExecTransformer explode(_pre_0#45), [emp_id#19, emp_name#20, dept_names#21, sale#22], false, [dept_name#36]
   :                                            +- ^(1) ProjectExecTransformer [emp_id#19, emp_name#20, dept_names#21, sale#22, split(dept_names#21, ,, -1) AS _pre_0#45]
   :                                               +- ^(1) InputIteratorTransformer[emp_id#19, emp_name#20, dept_names#21, sale#22]
   :                                                  +- RowToVeloxColumnar
   :                                                     +- LocalTableScan [emp_id#19, emp_name#20, dept_names#21, sale#22]
   +- ^(6) InputIteratorTransformer[emp_id#27, sum(sale)#40L]
      +- ColumnarBroadcastExchange HashedRelationBroadcastMode(List(cast(input[0, int, false] as bigint)),false), [plan_id=2116]
         +- ^(5) HashAggregateTransformer(keys=[emp_id#27], functions=[sum(sale#30)], isStreamingAgg=false)
            +- ^(5) InputIteratorTransformer[emp_id#27, sum#44L]
               +- ColumnarExchange hashpartitioning(emp_id#27, 2000), ENSURE_REQUIREMENTS, [emp_id#27, sum#44L], [plan_id=2097], [shuffle_writer_type=hash], [OUTPUT] List(emp_id:IntegerType, sum:LongType)
                  +- VeloxResizeBatches 1024, 2147483647, 10485760
                     +- ^(4) ProjectExecTransformer [hash(emp_id#27, 42) AS hash_partition_key#72, emp_id#27, sum#44L]
                        +- ^(4) FlushableHashAggregateTransformer(keys=[emp_id#27], functions=[partial_sum(sale#30)], isStreamingAgg=false)
                           +- ^(4) ProjectExecTransformer [emp_id#27, sale#30]
                              +- ^(4) HashAggregateTransformer(keys=[emp_id#27, emp_name#28, dept_names#29, sale#30], functions=[], isStreamingAgg=false)
                                 +- ^(4) InputIteratorTransformer[emp_id#27, emp_name#28, dept_names#29, sale#30]
                                    +- ReusedExchange [emp_id#27, emp_name#28, dept_names#29, sale#30], ColumnarExchange hashpartitioning(emp_id#19, emp_name#20, dept_names#21, sale#22, 2000), ENSURE_REQUIREMENTS, [emp_id#19, emp_name#20, dept_names#21, sale#22], [plan_id=1996], [shuffle_writer_type=hash], [OUTPUT] List(emp_id:IntegerType, emp_name:StringType, dept_names:StringType, sale:IntegerType)

There is a ReusedExchange in the plan, which is in expectation.

Side effect: after this PR, GenerateExec with generator offloadable will not fallback because the child of generator is Alias and its validation will always succeed.

[philo-he]

LGTM. Thanks.