Add NullBuffer::try_from_unsliced helper and refactor call sites

[Eyad3skr]

Implements a helper to replace the pattern of creating a BooleanBuffer from an unsliced validity bitmap and filtering by null count. Previously this was done with BooleanBuffer::new(...) plus Some(NullBuffer::new(...)).filter(|n| n.null_count() > 0); now it is a single call to NullBuffer::try_from_unsliced(buffer, len), which returns Some(NullBuffer) when there are nulls and None when all values are valid.

• Added try_from_unsliced in arrow-buffer/src/buffer/null.rs with tests for nulls, all valid, all null, empty
• Refactor FixedSizeBinaryArray::try_from_iter_with_size and try_from_sparse_iter_with_size to use it
• Refactor take_nulls in arrow-select to use it

Closes #9385

[alamb]

Thank you @Eyad3skr -- this looks nice to me

cc @liamzwbao in case you have time to help reivew

[alamb]

Could you also update this comment to reflect the offset is in bits (not bytes)? Mixing the units is a common mistake so making sure the documentation is as clear as possible would help