Move hash_array into hash_utils.rs

[alamb]

Which issue does this PR close?

Re #790 by implementing a new design for group by hash

Rationale for this change

1. The design in Rework GroupByHash for faster performance and support grouping by nulls #790 calls for hashing the input to group by hash in a manner almost-identical with create_hashes in hash_join, which I hope to reuse
2. It turns out the hashing algorithm is also used by repartition exec as well
3. I want to add additional coverage to the hash code (to ensure it is in sync with ScalarValue)

What changes are included in this PR?

Move create_hashes into hash_utils so it can be shared with hash_join and hash_aggregate.

Are there any user-facing changes?

No. This PR just moves code, No functional changes intended.

[Dandandan]

👍