[SQL] Preserve SELECT-list order when extracting multiple generators

[vladimirg-db]

What changes were proposed in this pull request?

This change makes ExtractGenerator preserve SELECT-list order when it extracts independent
generator expressions. A generator may still be extracted ahead of an earlier generator when the
earlier generator has a direct or transitive lateral-column-alias dependency on a generator to its
right.

The internal configuration spark.sql.generator.preserveSelectListOrder defaults to true for the
new behavior. Setting it to false restores the previous first-ready extraction behavior.

Why are the changes needed?

Generator extraction currently happens over multiple analyzer iterations. If a later generator's
children resolve before an earlier generator's children, the later generator is extracted first.
That changes the nesting and evaluation order of the resulting Generate operators. The difference
is observable when generator inputs contain nondeterministic expressions or UDFs and can change query
results.

Does this PR introduce any user-facing change?

Yes. Independent generators are now evaluated in SELECT-list order by default. For example, with an
identity UDF registered as udf:

SELECT
  explode(array(sin(0) + udf(monotonically_increasing_id()))) AS left_value,
  explode(array(10, 20)) AS right_value;

The new behavior returns (0.0, 10) and (0.0, 20). The previous behavior could return
(0.0, 10) and (1.0, 20) because the right generator was extracted first. Setting
spark.sql.generator.preserveSelectListOrder=false restores the previous behavior.

How was this patch tested?

Added SQL golden tests for both configuration values. They cover Scala and Python UDFs,
nondeterministic expressions, multiple generators, grouping analytics, direct and transitive
lateral-column-alias dependencies, and a case combining all of them.

build/sbt "sql/testOnly org.apache.spark.sql.SQLQueryTestSuite -- -z generators-resolution-edge-cases.sql"
build/sbt "sql/testOnly org.apache.spark.sql.SQLQueryTestSuite -- -z generator-ordering"

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