Clarify `rehash` setting in hash utils

### Is your feature request related to a problem or challenge?

In our hash util functions, we have a `rehash` argument across many of them:

https://github.com/apache/datafusion/blob/b80bf2ca8ef74900fee96a1cc169bdedf53b36fc/datafusion/common/src/hash_utils.rs#L185-L190

https://github.com/apache/datafusion/blob/b80bf2ca8ef74900fee96a1cc169bdedf53b36fc/datafusion/common/src/hash_utils.rs#L230-L235

https://github.com/apache/datafusion/blob/b80bf2ca8ef74900fee96a1cc169bdedf53b36fc/datafusion/common/src/hash_utils.rs#L282-L287

It's not clearly obvious why we do this from the code alone; it seems it used to be named `multi_col` and would be true if we needed to hash multiple columns, but was changed in #6816 to also skip rehash if it is the first column, for performance reasons.

- It seems dictionary function also still calls it `multi_col`

I also found it confusing how certain hash functions don't have a rehash parameter; specifically the nested types such as list, struct, etc.

https://github.com/apache/datafusion/blob/b80bf2ca8ef74900fee96a1cc169bdedf53b36fc/datafusion/common/src/hash_utils.rs#L447-L451

https://github.com/apache/datafusion/blob/b80bf2ca8ef74900fee96a1cc169bdedf53b36fc/datafusion/common/src/hash_utils.rs#L475-L479

https://github.com/apache/datafusion/blob/b80bf2ca8ef74900fee96a1cc169bdedf53b36fc/datafusion/common/src/hash_utils.rs#L510-L515

### Describe the solution you'd like

Add some documentation explaining why we have a `rehash` parameter across the functions. Also look into adding `rehash` parameter for those hash functions missing them. If this parameter was omitted on purpose for such functions, leave an explanation of why this is the case.

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

Inizia in datafusion/common/src/hash_utils.rs con le funzioni di hash intorno alle righe 185-190, 230-235 e 282-287, quindi esamina le funzioni per dizionari e tipi annidati intorno alle righe 447-451, 475-479 e 510-515. Controlla la cronologia di #6816 per comprendere il comportamento di rehash. Il lavoro è completato quando il parametro rehash è documentato in modo coerente e i parametri mancanti vengono aggiunti oppure viene spiegata la loro omissione intenzionale.

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