impl std::fmt::Write for StringViewBuilder / BinaryViewBuilder

[alamb]

Which issue does this PR close?

Closes #6373

Rationale for this change

@tlm365 is trying to implement cast from various types to StringView efficiently in

• [arrow-cast] Support cast from Numeric (Int, UInt, etc) to Utf8View #6719

Also, DataFusion had several places where it would like to write to a StringViewBuilder using standard rust formatting such as write!

What changes are included in this PR?

1. impl std::fmt::Write for StringViewBuilder / BinaryViewBuilder
2. Tests + documentation

Open questions / follow on PRs:

1. Should I implement the same sort of "finish the row on drop" style API for StringBuilder

Are there any user-facing changes?

Yes, new APIs + docs

[tustvold]

I think this will perform identically to just writing to a temporary String manually?

I wonder if we could do something a bit more sophisticated, but then again perhaps it won't make a difference.

I like the Drop based flush, although it does introduce a bit of API inconsistency...