Core: Enforce that v4 manifests do not contain POSITION_DELETES

[yadavay-amzn]

Fixes #16340.

Follow-up from PR #16100 discussion.

Problem

The Variant v4 format uses deletion vectors instead of positional delete files. TrackedFileStruct currently accepts POSITION_DELETES content type without validation, and V4Metadata includes fields (REFERENCED_DATA_FILE, CONTENT_OFFSET, CONTENT_SIZE) that are only relevant to positional deletes.

Fix

1. TrackedFileStruct: Add validation in internalSet to reject FileContent.POSITION_DELETES with a clear error message.
2. V4Metadata: Remove positional-delete-specific fields from the file type schema and remove POSITION_DELETES handling from DataFileWrapper.get().

Testing

• Added testPositionDeletesRejected verifying IllegalArgumentException when attempting to set POSITION_DELETES content type.
• Updated testAllFileContentTypesSupported to skip POSITION_DELETES for v4.
• All existing manifest tests pass.

[yadavay-amzn]

Closing -- the issue was resolved separately. Thanks.