Fix missing includes

These and more will become apparent once
firebase/firebase-ios-sdk#4868 lands.

PiperOrigin-RevId: 297639952

Author: wilhuff

firestore/src/ios/document_snapshot_ios.cc

@@ -11,6 +11,7 @@
 #include "Firestore/core/src/firebase/firestore/model/document_key.h"
 #include "Firestore/core/src/firebase/firestore/model/field_path.h"
 #include "Firestore/core/src/firebase/firestore/model/field_value_options.h"
+#include "Firestore/core/src/firebase/firestore/nanopb/byte_string.h"
 
 namespace firebase {
 namespace firestore {

firestore/src/ios/field_value_ios.cc

@@ -5,6 +5,7 @@
 #include "firestore/src/include/firebase/firestore/map_field_value.h"
 #include "firestore/src/ios/converter_ios.h"
 #include "firestore/src/ios/hard_assert_ios.h"
+#include "Firestore/core/src/firebase/firestore/nanopb/byte_string.h"
 
 namespace firebase {
 namespace firestore {