### What changes were proposed in this pull request?
Current AQE has cost evaluator to decide whether to use new plan after replanning. The current used evaluator is `SimpleCostEvaluator` to make decision based on number of shuffle in the query plan. This is not perfect cost evaluator, and different production environments might want to use different custom evaluators. E.g., sometimes we might want to still do skew join even though it might introduce extra shuffle (trade off resource for better latency), sometimes we might want to take sort into consideration for cost as well. Take our own setting as an example, we are using a custom remote shuffle service (Cosco), and the cost model is more complicated. So We want to make the cost evaluator to be pluggable, and developers can implement their own `CostEvaluator` subclass and plug in dynamically based on configuration.
The approach is to introduce a new config to allow define sub-class name of `CostEvaluator` - `spark.sql.adaptive.customCostEvaluatorClass`. And add `CostEvaluator.instantiate` to instantiate the cost evaluator class in `AdaptiveSparkPlanExec.costEvaluator`.
### Why are the changes needed?
Make AQE cost evaluation more flexible.
### Does this PR introduce _any_ user-facing change?
No but an internal config is introduced - `spark.sql.adaptive.customCostEvaluatorClass` to allow custom implementation of `CostEvaluator`.
### How was this patch tested?
Added unit test in `AdaptiveQueryExecSuite.scala`.
Closes#32944 from c21/aqe-cost.
Authored-by: Cheng Su <chengsu@fb.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
044dddf288