make builder public under experimental (#7825)

Make `ArrayReaderBuilder` public (under experimental), I think the
ability to build array reader was public prior to
#7521

This will allow downstream users to build their own array readers. This
is also consistent with many other array readers that are public.

Author: XiangpengHao

parquet/src/arrow/array_reader/builder.rs

@@ -35,12 +35,12 @@ use crate::errors::{ParquetError, Result};
 use crate::schema::types::{ColumnDescriptor, ColumnPath, Type};
 
 /// Builds [`ArrayReader`]s from parquet schema, projection mask, and RowGroups reader
-pub(crate) struct ArrayReaderBuilder<'a> {
+pub struct ArrayReaderBuilder<'a> {
     row_groups: &'a dyn RowGroups,
 }
 
 impl<'a> ArrayReaderBuilder<'a> {
-    pub(crate) fn new(row_groups: &'a dyn RowGroups) -> Self {
+    pub fn new(row_groups: &'a dyn RowGroups) -> Self {
         Self { row_groups }
     }
 

parquet/src/arrow/array_reader/mod.rs

@@ -45,7 +45,8 @@ mod struct_array;
 #[cfg(test)]
 mod test_util;
 
-pub(crate) use builder::ArrayReaderBuilder;
+// Note that this crate is public under the `experimental` feature flag.
+pub use builder::ArrayReaderBuilder;
 pub use byte_array::make_byte_array_reader;
 pub use byte_array_dictionary::make_byte_array_dictionary_reader;
 #[allow(unused_imports)] // Only used for benchmarks