use FileFormat::get_ext as the default file extension filter

[waruto210]

Which issue does this PR close?

Closes #12378.

Rationale for this change

Using FileFormat::get_ext as the default file extension filter better meets user expectations.

What changes are included in this PR?

Use FileFormat::get_ext as the default file extension filter

Are these changes tested?

Yes

Are there any user-facing changes?

User do not need to specify the file extension if they choose the default value.

[alamb]

Thank you @waruto210 -- this makes sense to me and I think is a nice improvement.

I have a small API improvement suggestion, but I think we can do it as a follow on PR if you prefer.

Thanks again!

[alamb]

Maybe we could make this a nicer API by adding with_file_extension_opt or something so this code could be like:

let opt = ListingOptions::new(Arc::new(format))
            .with_file_extension_opt(file_ext)
            .with_target_partitions(target_partitions);

[waruto210]

Maybe we could make this a nicer API by adding with_file_extension_opt or something so this code could be like:

let opt = ListingOptions::new(Arc::new(format))
            .with_file_extension_opt(file_ext)
            .with_target_partitions(target_partitions);

I think your advice is great, I'm on vacation right now and I'll revise the code when I get back.

[alamb]

Here is a PR with the proposed API: #12461

[waruto210]

Here is a PR with the proposed API: #12461

I have modified the code according to this API.

[alamb]

BTW I am holding off on merging this PR until we cut the 42 release candidate to avoid introducing last minute behavior changes

[alamb]

Thanks @waruto210 -- this is great. 🚀