[SPARK-32499][SQL] Use {} in conversions maps and structs to strings

[MaxGekk]

What changes were proposed in this pull request?

Change casting of map and struct values to strings by using the {} brackets instead of []. The behavior is controlled by the SQL config spark.sql.legacy.castComplexTypesToString.enabled. When it is true, CAST wraps maps and structs by [] in casting to strings. Otherwise, if this is false, which is the default, maps and structs are wrapped by {}.

Why are the changes needed?

• To distinguish structs/maps from arrays.
• To make show's output consistent with Hive and conversions to Hive strings.
• To display dataframe content in the same form by spark-sql and show
• To be consistent with the *.sql tests

Does this PR introduce any user-facing change?

Yes

How was this patch tested?

By existing test suite CastSuite.

[SparkQA]

Test build #126805 has finished for PR 29308 at commit 117b276.

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

[MaxGekk]

@maropu @cloud-fan Please, review this PR.

[maropu]

Looks good.

[SparkQA]

Test build #126977 has finished for PR 29308 at commit 77b6637.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #126991 has finished for PR 29308 at commit c494628.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #127007 has finished for PR 29308 at commit 168dc00.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
• case class ExecutorProcessLost(
• case class RegExpExtractAll(subject: Expression, regexp: Expression, idx: Expression)
• .doc(\"The name of a class that implements \" +
• trait CachedBatch
• trait CachedBatchSerializer extends Serializable
• trait SimpleMetricsCachedBatch extends CachedBatch
• abstract class SimpleMetricsCachedBatchSerializer extends CachedBatchSerializer with Logging
• case class ColumnarToRowExec(child: SparkPlan) extends ColumnarToRowTransition with CodegenSupport
• case class ApplyColumnarRulesAndInsertTransitions(
• class ColumnStatisticsSchema(a: Attribute) extends Serializable
• class PartitionStatistics(tableSchema: Seq[Attribute]) extends Serializable
• case class DefaultCachedBatch(numRows: Int, buffers: Array[Array[Byte]], stats: InternalRow)
• class DefaultCachedBatchSerializer extends SimpleMetricsCachedBatchSerializer
• trait HashJoin extends BaseJoinExec with CodegenSupport

[SparkQA]

Test build #127035 has finished for PR 29308 at commit 138b73c.

• This patch fails due to an unknown error code, -9.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #127042 has finished for PR 29308 at commit ae35de3.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #127048 has finished for PR 29308 at commit 91acda1.

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

[cloud-fan]

thanks, merging to master!