Introduce `NullBuffer::try_from_unsliced` to simplify array construction

[liamzwbao]

This pattern of creating a BooleanBuffer from with a length and then filtering for nulls count is quite common (and becoming more so)

I wonder if we should (as a follow on PR) make a function to do it, maybe like

let Option<NullBuffer> = NullBuffer::try_from_unsliced(b, array.len())

Then this code would look like

let nulls = array
        .nulls()
        .map(|n| n.inner().sliced())
        .map(|b| NullBuffer::try_from_unsliced(b, array.len()

🤔

Originally posted by @alamb in #9338 (comment)

[Eyad3skr]

Hey, I’d like to take this one. I’ll work on adding the NullBuffer helper + tests, then update a few call sites

[alamb]

Sounds like a good plan -- thank you