arrow-cast: Support cast to Dictionary<_, FixedSizeBinary> and add FixedSizeBinaryDictionaryBuilder

[metalmatze]

Which issue does this PR close?

Closes #6665.

Rationale for this change

The added code seems to be where the casting and packing is handled.

What changes are included in this PR?

Are there any user-facing changes?

No, I don't think so.

[tustvold]

Can you add tests please

[alamb]

Marking as draft as this is not waiting on any more feedback -- please mark it as ready for review when it is time.

Extending the existing tests should be straightforward -- let us know if you need help @metalmatze

Thanks for the contribution

[metalmatze]

Thanks, everyone!
Happy to add tests.
I couldn't find any initially, and now I can't seem to find the ones you're referencing. Are they in a different directory?

[alamb]

Thanks, everyone! Happy to add tests. I couldn't find any initially, and now I can't seem to find the ones you're referencing. Are they in a different directory?

Perhaps you could follow the model of

arrow-rs/arrow-cast/src/cast/mod.rs

Line 6795 in 3ee5048

fn test_cast_utf8_dict() {

?

[metalmatze]

I've added tests and it's ready for another round of reviews!

[alamb]

Thank you very much for this contribution @metalmatze

In order to unstall this PR as it has been sitting for so long, I took the liberty of pushing a few commits to this PR:

1. Add test that cast deduplicated values
2. A doc example
3. Some fixes for clippy
4. An error test for values of the wrong length

[metalmatze]

Thank you for taking it across the finish line! Much appreciated! LGTM and it's great to learn from.