## What changes were proposed in this pull request?
This patch defines an internal Spark interface for reporting shuffle metrics and uses that in shuffle reader. Before this patch, shuffle metrics is tied to a specific implementation (using a thread local temporary data structure and accumulators). After this patch, callers that define their own shuffle RDDs can create a custom metrics implementation.
With this patch, we would be able to create a better metrics for the SQL layer, e.g. reporting shuffle metrics in the SQL UI, for each exchange operator.
Note that I'm separating read side and write side implementations, as they are very different, to simplify code review. Write side change is at https://github.com/apache/spark/pull/23106
## How was this patch tested?
No behavior change expected, as it is a straightforward refactoring. Updated all existing test cases.
Closes#23105 from rxin/SPARK-26140.
Authored-by: Reynold Xin <rxin@databricks.com>
Signed-off-by: gatorsmile <gatorsmile@gmail.com>
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