libbinder*: toString - support unique_ptr

Exists for @nullable(heap=true)

Bug: 259162245
Test: make AIDL RecursiveList when toString functions
  are a compilation requirement
Change-Id: I5d589d7501423b850758126e541074047cb99b4c
diff --git a/libs/binder/ndk/include_cpp/android/binder_to_string.h b/libs/binder/ndk/include_cpp/android/binder_to_string.h
index 8d3231d..27fdcdb 100644
--- a/libs/binder/ndk/include_cpp/android/binder_to_string.h
+++ b/libs/binder/ndk/include_cpp/android/binder_to_string.h
@@ -111,10 +111,12 @@
             IsInstantiationOf<_U, sp>::value ||  // for IBinder and interface types in the C++
                                                  // backend
 #endif
-                    IsInstantiationOf<_U, std::optional>::value ||  // for @nullable types in the
-                                                                    // C++/NDK backends
-                    IsInstantiationOf<_U, std::shared_ptr>::value,  // for interface types in the
-                                                                    // NDK backends
+                    IsInstantiationOf<_U, std::optional>::value ||    // for @nullable types in the
+                                                                      // C++/NDK backends
+                    IsInstantiationOf<_U, std::unique_ptr>::value ||  // for @nullable(heap=true)
+                                                                      // in C++/NDK backends
+                    IsInstantiationOf<_U, std::shared_ptr>::value,    // for interface types in the
+                                                                      // NDK backends
 
             std::true_type>
     _test(int);