Collection types in FROM clause for Iceberg Metadata Tables

Iceberg Metadata Table Collection types are not supported in from clause, therefore it is not possible to use 'item' or 'pos' in case of arrays for example.

Example query:

select delete_ids.item
from functional_parquet.iceberg_query_metadata.all_files, functional_parquet.iceberg_query_metadata.all_files.equality_ids delete_ids; 

When scanning metadata tables, the whole table and row is read from Iceberg which means that the "top" level StructLikeRow is returned. But Impala only creates tuples and slots for the selected slots and tuples. This makes accessing the values inside StructLikeRows difficult, because it cannot be accessed through accessors and these have to be accessed through positions.