feat: support arrow_struct_to_iceberg_struct (#731)

This PR introduces the function to convert arrow struct to iceberg
struct. This function is needed when we add fanout partition writer: In
this writer, we need to compute the partition value using record batch
and convert them into struct value finally and set into data file.

---------

Co-authored-by: ZENOTME <[email protected]>

Author: ZENOTME

crates/iceberg/src/arrow/mod.rs

@@ -22,5 +22,6 @@ pub use schema::*;
 mod reader;
 pub(crate) mod record_batch_projector;
 pub(crate) mod record_batch_transformer;
-
+mod value;
 pub use reader::*;
+pub use value::*;

crates/iceberg/src/arrow/schema.rs

@@ -226,7 +226,7 @@ pub fn arrow_type_to_type(ty: &DataType) -> Result<Type> {
 
 const ARROW_FIELD_DOC_KEY: &str = "doc";
 
-fn get_field_id(field: &Field) -> Result<i32> {
+pub(super) fn get_field_id(field: &Field) -> Result<i32> {
     if let Some(value) = field.metadata().get(PARQUET_FIELD_ID_META_KEY) {
         return value.parse::<i32>().map_err(|e| {
             Error::new(