[SPARK-56125][SQL] Simplify schema calculation for Merge Into Schema Evolution#54934

szehon-ho wants to merge 2 commits intoapache:masterapache/spark:masterfrom

szehon-ho:SPARK-55690-merge-pending-schema-changes-refactorszehon-ho/spark:SPARK-55690-merge-pending-schema-changes-refactorCopy head branch name to clipboard