`filter_push_down` panics on semi/anti join with join filters

[andygrove]

Is your feature request related to a problem or challenge? Please describe what you are trying to do. Since merging https://github.com/apache/arrow-datafusion/commit/ae6dab0d161ba889ae97a304172f06576614aa48 we support join filters on semi/anti joins, although this won't be exposed to end-users until https://github.com/apache/arrow-datafusion/pull/2885 is merged.

The following code is not correct:

            // Semi/Anti joins can not have join filter.
            JoinType::Semi | JoinType::Anti => unreachable!(
                "on_lr_is_preserved cannot be appplied to SEMI/ANTI-JOIN nodes"
            ),

Describe the solution you'd like Not sure what the solution is but we shouldn't panic.

Describe alternatives you've considered None

Additional context None