Describe the bug

Currently the output ordering -- which is defined per partition -- is a vector of LexOrdering:

This was kinda OK before #16217 because LexOrdering was allowed to be empty -- which was basically a sentinel value for "not ordering". Now however the code cannot specify that a partition isn't ordered anymore. This actually leads to some funky bugs like in this code here:

So if the projection for a single partition leads to "unordered", then get_projected_output_ordering(input).len() < input.len(), i.e. we loose partitions. This can clearly not be right.

To Reproduce

No response

Expected behavior

FileScanConfig::output_ordering must be Vec<Option<LexOrdering>>.

Additional context

No response