Fix input_dist for when it has to handle KVZCH and non-KVZCH tables together for row-wise sharding (#3444)

Summary:

In the KVZCH scenarios, the input_dist for row-wise sharding will have to deal with KVZCH and non-KVZCH features together. This means that the virtual_table_feature_num_buckets will have to represent non-KVZCH features too.
In this diff, we default the value of the num_buckets to world_size for non-KVZCH features.

Differential Revision: D84094039

Author: nipung90

torchrec/distributed/sharding/rw_sharding.py

@@ -301,6 +301,11 @@ def _get_writable_feature_hash_sizes(self) -> List[int]:
         return feature_hash_sizes
 
     def _get_virtual_table_feature_num_buckets(self) -> List[int]:
+        """
+        Returns the number of buckets for each KVZCH feature in the GroupedEmbeddingConfigs.
+        If a feature is not a KVZCH feature, the list will have world_size for that feature's corresponding position.
+        This is needed as KVZCH features have to be processed for input_dist with non-KVZCH features.
+        """
         feature_num_buckets: List[int] = []
         for group_config in self._grouped_embedding_configs:
             for embedding_table in group_config.embedding_tables:
@@ -312,6 +317,10 @@ def _get_virtual_table_feature_num_buckets(self) -> List[int]:
                         [embedding_table.total_num_buckets]
                         * embedding_table.num_features()
                     )
+                else:
+                    feature_num_buckets.extend(
+                        [self._world_size] * embedding_table.num_features()
+                    )
         return feature_num_buckets