Add DataType::Utf8View and DataType::BinaryView

[XiangpengHao]

Which issue does this PR close?

Part of #5468 .

Closes #5468

Rationale for this change

Add DataType::Utf8View and DataType::BinaryView. This is the first step towards supporting StringViewArray in arrow.

What changes are included in this PR?

Only the type definition and the related comments. Most of the handling of the types are unimplemented!()

I'm new to arrow and not sure if this is the commit granularity we expected, comments/suggestions welcome!

Are there any user-facing changes?

[alamb]

Thank you @XiangpengHao

I was going to suggest returning errors rather than panic but now I see that the apis aren't fallible (don't return Results).

Thus, even though using unimplemented! will panic, I think this is ok for now and is consistent with what we did with other array types that didn't have full support.

Another potential alternative is to make a feature flag and #[feature(array_view))] all the relevant call sites

However, if others think it is important not to panic in the API, I suggest we make a feature branch (I can do so) and we can merge PRs to that feature branch while in development and then merge the feature branch to master when it is ready

[alamb]

This is a good reminder that we need to implement IPC support as well -- I added that as a task to

[alamb]

I am pleasantly surprised by how few places in the code needed to be changed.

[alamb]

Looks great to me -- thank you @XiangpengHao

I left some suggestions on wording, but

I think we should leave this PR open for at least 24 hours to give other people a chance to comment

[tustvold]

Panicking is fine imo whilst we get this integrated. I would recommend changing the unimplemented! messages to state what isn't implemented

[XiangpengHao]

I am pleasantly surprised by how few places in the code needed to be changed.

I mostly rely on the compiler to find where to add unimplemented!(). Other cases like:

match data_type {
  DataType::some_thing => {}
  _ => {}
}

https://github.com/XiangpengHao/arrow-rs/blob/d861177a5d0171fab8d4f646d3b72dfabf83b14d/rust/arrow/src/datatypes/field.rs#L124

Might require a closer look to make sure they are safe to escape

[ariesdevil]

If there's nothing wrong with it, let's go ahead and merge it and I'll do a follow-up based on that.

[alamb]

THanks everyone -- it is so exciting to see this project begin

Also, kudos to @XiangpengHao for your first Arrow contribution!