Bitmap Length Validation is Incorrect

[tustvold]

Describe the bug

Noticed whilst testing #1230, the bitmask length validation confuses byte length and bit length.

This will allow bitmasks that are too short to pass ArrayData::try_new validation

To Reproduce

#[test]
    fn test_validate_bitmask_length() {
        let data = MutableBuffer::from_len_zeroed(9 * 4).into();
        let nulls = MutableBuffer::new_null(1).into();

        let err = ArrayData::try_new(
            DataType::Int32,
            9,
            Some(9),
            Some(nulls),
            0,
            vec![data],
            vec![],
        )
        .unwrap_err()
        .to_string();

        assert!(
            err.contains("null_bit_buffer size too small. got 1 needed 2"),
            "{}",
            err
        )
    }

Expected behavior

The above test should pass