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ARROW-10381: [Rust] Generalized Ordering for inter-array comparisons

Currently, the code on `array/ord.rs` is centered around intra-array comparison. However, this does not allow to compare values from two different arrays, which is required on e.g. merge-sort operations.

This PR:
* simplifies the code around `sort` by splitting it in smaller functions for ease of understanding (first 2 commits)
* adds a benchmark to the `sort` kernel which I used to verify that there was no performance regression  (3rd commit)
* simplifies and generalizes the code around `ord` to support comparisons between two arrays (that may be the same), 4th commit
* adds some more tests to edge cases around float comparison (nan and zeros)

There was no performance change on my computer.

Closes #8517 from jorgecarleitao/sort

Authored-by: Jorge C. Leitao <jorgecarleitao@gmail.com>
Signed-off-by: Jorge C. Leitao <jorgecarleitao@gmail.com>