Use credential_id to correlate matched credential back to original

Upon succesfully dectypting an advertisements, the decoding library returns the id of the credential which was used to decrypt. We then use this id to correlate the decoded adv back to the original shared_credential which was used to decrypt it and save this and propagate it in the result returned to the caller

PiperOrigin-RevId: 646179759

presence/implementation/advertisement_decoder_rust_impl.h

@@ -29,13 +29,19 @@ namespace presence {
 // Implements the Rust backed parsing and decrypting of advertisement bytes
 class AdvertisementDecoderImpl : public AdvertisementDecoder {
  public:
-  AdvertisementDecoderImpl() : cred_book_(InitializeCredentialBook(nullptr)) {}
+  AdvertisementDecoderImpl()
+      : cred_book_(InitializeCredentialBook(nullptr)),
+        private_credentials_(
+            std::vector<::nearby::internal::SharedCredential>()) {}
 
   explicit AdvertisementDecoderImpl(
       absl::flat_hash_map<nearby::internal::IdentityType,
                           std::vector<internal::SharedCredential>>*
           credentials_map)
-      : cred_book_(InitializeCredentialBook(credentials_map)) {}
+      : cred_book_(InitializeCredentialBook(credentials_map)),
+        private_credentials_(
+            (*credentials_map)
+                [internal::IdentityType::IDENTITY_TYPE_PRIVATE_GROUP]) {}
 
   absl::StatusOr<Advertisement> DecodeAdvertisement(
       absl::string_view advertisement) override;
@@ -46,6 +52,7 @@ class AdvertisementDecoderImpl : public AdvertisementDecoder {
                           std::vector<::nearby::internal::SharedCredential>>*
           credentials_map);
   nearby_protocol::CredentialBook cred_book_;
+  std::vector<::nearby::internal::SharedCredential> private_credentials_;
 };
 
 }  // namespace presence