[SPARK-11849][SQL] Analyzer should replace current_date and current_timestamp with literals

[rxin]

We currently rely on the optimizer's constant folding to replace current_timestamp and current_date. However, this can still result in different values for different instances of current_timestamp/current_date if the optimizer is not running fast enough.

A better solution is to replace these functions in the analyzer in one shot.

[rxin]

cc @cloud-fan

[cloud-fan]

nit: space before {

[rxin]

k updated.

[SparkQA]

Test build #46311 has finished for PR 9833 at commit 33013e6.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):\n * public final class UnsafeSorterSpillReader extends UnsafeSorterIterator implements Closeable\n * class Pipeline(override val uid: String) extends Estimator[PipelineModel] with MLWritable\n * class CountVectorizerModelWriter(instance: CountVectorizerModel) extends MLWriter\n * final class IDF(override val uid: String) extends Estimator[IDFModel] with IDFBase\n * class MinMaxScalerModelWriter(instance: MinMaxScalerModel) extends MLWriter\n * class SQLTransformer @Since(\"1.6.0\") (override val uid: String) extends Transformer\n * class StandardScalerModelWriter(instance: StandardScalerModel) extends MLWriter\n * class StringIndexModelWriter(instance: StringIndexerModel) extends MLWriter\n * class ALS(override val uid: String) extends Estimator[ALSModel] with ALSParams\n * abstract class MLWriter extends BaseReadWrite with Logging\n * trait MLWritable\n * abstract class MLReader[T] extends BaseReadWrite\n * trait MLReadable[T]\n * trait ScalaReflection\n * case class Schema(dataType: DataType, nullable: Boolean)\n * s\"Unable to generate an encoder for inner class$\n *public abstract class SpecificParquetRecordReaderBase extends RecordReader<Void, T> \n * abstract static class IntIterator \n * protected static final class ValuesReaderIntIterator extends IntIterator \n * protected static final class RLEIntIterator extends IntIterator \n * protected static final class NullIntIterator extends IntIterator \n *public class UnsafeRowParquetRecordReader extends SpecificParquetRecordReaderBase `\n

[SparkQA]

Test build #46319 has finished for PR 9833 at commit 1ddbe84.

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

[cloud-fan]

LGTM

[rxin]

Merging this. Thanks.