Add TrackedFile adapter for v2 position delete files

[anoopj]

Feature Request / Improvement

Context

TrackedFileAdapters currently provides adapters for:

• asDataFile -- wraps a DATA TrackedFile as a DataFile
• asEqualityDeleteFile -- wraps an EQUALITY_DELETES TrackedFile as a DeleteFile
• asDVDeleteFile -- extracts the DV from a DATA TrackedFile as a DeleteFile

There is no adapter for v2-style position delete files (content type
POSITION_DELETES). Tables upgraded from v2 to v4 may still contain position
delete files that were written before the upgrade, and scan planning needs
to wrap these as DeleteFile instances.

See #16100 (comment)

Proposed change

Add asPositionDeleteFile(TrackedFile, Map<Integer, PartitionSpec>) to
TrackedFileAdapters. This can extend AbstractTrackedContentFile<DeleteFile>
with:

• content() returning FileContent.POSITION_DELETES
• firstRowId() returning null (per spec, first_row_id for delete files is always null)
• equalityFieldIds() returning null

Query engine

None

Willingness to contribute

• I can contribute this improvement/feature independently
• I would be willing to contribute this improvement/feature with guidance from the Iceberg community
• I cannot contribute this improvement/feature at this time

[anoopj]

Working on this