[built-in function] add `greatest(T,...)` and `least(T,...)` SQL functions

[jimexist]

Which issue does this PR close?

• Closes #6531

Rationale for this change

add greatest(T,..) and least(T,..) variadic functions as per SQL 2023.

What changes are included in this PR?

• add greatest(T,..) and least(T,..) variadic functions as per SQL 2023.
  • when no args are supplied the functions err
  • when both scalar and arrays are supplied then scalars are converted to arrays before max/min
  • only boolean, string, and numeric types are supported for now, no dates, etc.
  • arrow zip and ord kernels are used
• change variadic equal function signature to take a vec of allowed types, only types within that types can be used

Are these changes tested?

• unit tests
• integration tests using tokio and based on sql

Are there any user-facing changes?

[alamb]

Marking as draft as this PR has feedback and is awaiting a response (I am trying to keep the list of PRs needing review clear) -- please mark as ready for review when ready

[jimexist]

Welcome back 👋 @Jimexist ! It is great to see you again and thank you for your contribution.

I am sorry I wrote a comment about using Min and Max accumulators previously but I forgot to click submit.

cc @izveigor as I think you have been working to add additional support for array computations

thank you @alamb my bandwidth recently is very limited, so I am going to pause this PR for a bit, if anyone wants to take over feel free to. I can also do a merge as is (after rebase fix) and create issues as follow ups?

[alamb]

thank you @alamb my bandwidth recently is very limited, so I am going to pause this PR for a bit, if anyone wants to take over feel free to. I can also do a merge as is (after rebase fix) and create issues as follow ups?

Whatever you prefer -- I defer to your judgement

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