[Bug] next_day cross-version divergence: ANSI default flip and error class change between Spark 3.5 and 4.x

[andygrove]

Describe the bug

next_day behaves differently across the Spark versions datafusion-spark
targets, and DataFusion's .slt files have no way to express a
version-specific expectation. This issue records the divergence so it can be
scheduled once that mechanism exists.

Companion to #23887.

The divergence

Given a non-NULL start date and an unparseable day_of_week:

Spark version	Default spark.sql.ansi.enabled	Default result	Error class when ANSI is on
3.5.8	false	NULL	_LEGACY_ERROR_TEMP_2000, wrapped by QueryExecutionErrors.ansiIllegalArgumentError
4.0.4	true	error	ILLEGAL_DAY_OF_WEEK, SQLSTATE 22009
4.1.3	true	error	ILLEGAL_DAY_OF_WEEK, SQLSTATE 22009
4.2.0	true	error	ILLEGAL_DAY_OF_WEEK, SQLSTATE 22009

Two independent changes landed in Spark 4.0:

1. ANSI mode became the default, so the default result for the same query
   flipped from NULL to an error.
2. DateTimeUtils.getDayOfWeekFromString changed from
   throw new IllegalArgumentException("Illegal input for day of week: ...")
   to throw new SparkIllegalArgumentException(errorClass = "ILLEGAL_DAY_OF_WEEK", ...),
   and NextDay.nullSafeEval changed from catching IllegalArgumentException
   and re-wrapping to catching SparkIllegalArgumentException and rethrowing
   unchanged.

A third 4.0 change is not currently observable: inputTypes moved from
Seq(DateType, StringType) to
Seq(DateType, StringTypeWithCollation(supportsTrimCollation = true)).
datafusion-spark has no collation support, so there is nothing to diverge
from yet, but a non-default collation on the day_of_week argument is a
divergence axis that exists only in Spark 4.x.

Current state in DataFusion

Both modes are now implemented and tested behind
datafusion.execution.enable_ansi_mode, whose default is false. Anyone
comparing against a stock Spark 4.x will see DataFusion's default disagree with
Spark's default. The .slt file asserts Spark 4.2.0 behavior in each mode and
carries a comment naming the versions.

DataFusion does not model Spark error classes, so
_LEGACY_ERROR_TEMP_2000 versus ILLEGAL_DAY_OF_WEEK is not represented at
all. datafusion-spark raises
Execution error: Illegal input for day of week: <input>, matching Spark's
message text but not its error class or SQLSTATE.

Additional context

Relevant files:

• datafusion/spark/src/function/datetime/next_day.rs
• datafusion/sqllogictest/test_files/spark/datetime/next_day.slt
• Spark: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/datetimeExpressions.scala, case class NextDay
• Spark: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/DateTimeUtils.scala, getDayOfWeekFromString

Surfaced by the audit-datafusion-spark-expression skill.