Scan extension columns over list, map, and string storage in DataFusion - #11225

Summary

• Tracking Issue: Tracking Issue: Fix Extension Types #11114

DataFusion can't scan a Vector column today. Arrow carries an extension column as its storage plus field metadata, but the physical schema compares the table's Arrow layout with the extension dtype instead of its storage, so any extension column over list, map, or string storage fails before the scan reads a row. The same bug breaks a Json column that the table schema declares as Utf8.

Changes

The layout checks now look through extension types, as the struct check already did. An extension column keeps the table's layout (e.g., Utf8 rather than Utf8View for Json) instead of the type that ArrowSession would export for it, because the V2 source has no schema adapter, so its batches must match the plan schema exactly.

The Arrow map export returns an error instead of panicking on a dtype other than a map, as the list exporters already do, since an extension column over map storage can reach it now.

Note that this only helps types with an Arrow export plugin, such as Vector and Json, until #11224 exports the other types as their storage. A table field without the extension name now reads a Json or Vector column as plain storage (against X24), and #11268 makes that fail, so the two PRs should merge together.

Tests cover a SQL scan of a Vector column, a V2 projection over a Json column, each layout check of the physical schema, and the map export of a non-map array.