test: add sqllogictest coverage for DISTINCT / GROUP BY / aggregation on map columns

[PG1204]

Which issue does this PR close?

• Closes select distinct on map types yields ArrowError NotYetImplemented #15428.

Rationale for this change

SELECT DISTINCT on map columns used to fail with ArrowError(NotYetImplemented) because arrow-rs's RowConverter did not support Map types. That support has since landed upstream (apache/arrow-rs#7879) and is available on DataFusion main via arrow 59.1, so these queries now work. As suggested in #15428 (comment) (maintainer comment), this PR adds sqllogictest coverage to lock in the behavior and close the issue.

What changes are included in this PR?

Adds a new test section to datafusion/sqllogictest/test_files/map.slt covering:

• SELECT DISTINCT on a map column, including the exact reproducer from the issue (DISTINCT ... LIMIT), collapsing of duplicate maps and duplicate NULLs, and DISTINCT over map + scalar columns together
• GROUP BY on a map column, GROUP BY map + scalar keys, and HAVING with a map grouping key
• Aggregations with map inputs: COUNT(map), COUNT(DISTINCT map), SUM grouped by map, and array_agg of map values
• Edge cases: empty maps under DISTINCT (equal to each other, distinct from NULL), NULL maps, and unsorted maps with the same entries in different order being treated as distinct values
• UNION (distinct) on map columns
• DISTINCT / GROUP BY over the existing 209-row parquet_map.parquet file for coverage on real Parquet-backed map data

Note: a bare MAP {'key': NULL} literal infers a Null value type and fails type coercion across a VALUES list against Map(Utf8, Int64) rows, so the test uses CAST(NULL AS BIGINT) for the null map value. That coercion gap may be worth a separate follow-up issue.

Are these changes tested?

Yes, this PR is test-only. All tests pass locally via cargo test -p datafusion-sqllogictest --test sqllogictests -- map.slt.

Are there any user-facing changes?

No. Test-only change; no API or behavior changes.