[SPARK-29295][SQL][FOLLOWUP] Dynamic partition map parsed from partition path should be case insensitive

[turboFei]

What changes were proposed in this pull request?

This is a follow up of #25979.
When we inserting overwrite an external hive partitioned table with upper case dynamic partition key, exception thrown.

like:

org.apache.spark.SparkException: Dynamic partition key P1 is not among written partition paths.

The root cause is that Hive metastore is not case preserving and keeps partition columns with lower cased names, see details in:

spark/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveExternalCatalog.scala

Lines 895 to 901 in ddd8d5f

	// Hive metastore is not case preserving and keeps partition columns with lower cased names,
	// and Hive will validate the column names in partition spec to make sure they are partition
	// columns. Here we Lowercase the column names before passing the partition spec to Hive
	// client, to satisfy Hive.
	// scalastyle:off caselocale
	orderedPartitionSpec.put(colName.toLowerCase, partition(colName))
	// scalastyle:on caselocale

spark/sql/hive/src/main/scala/org/apache/spark/sql/hive/execution/InsertIntoHiveTable.scala

Lines 228 to 234 in e289140

	val updatedPartitionSpec = partition.map {
	case (key, Some(value)) => key -> value
	case (key, None) if dpMap.contains(key) => key -> dpMap(key)
	case (key, _) =>
	throw new SparkException(s"Dynamic partition key $key is not among " +
	"written partition paths.")
	}

In this PR, we convert the dynamic partition map to a case insensitive map.

Why are the changes needed?

To fix the issue when inserting overwrite into external hive partitioned table with upper case dynamic partition key.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

UT.

[turboFei]

cc @viirya @cloud-fan

[turboFei]

thanks, have added a blank line

[cloud-fan]

ok to test

[SparkQA]

Test build #123685 has finished for PR 28765 at commit d949065.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[cloud-fan]

thanks, merging to master/3.0!