Use std::optional for nullable

AIDL now use std::optional to represent nullable types for efficiency
instead of std::unique_ptr which might cause additional heap allocation.

Bug: 1447732670
Test: m
Change-Id: I9045bc6fc2eb06839203af6db94a80de9b83ad1f
diff --git a/services/camera/libcameraservice/api1/CameraClient.h b/services/camera/libcameraservice/api1/CameraClient.h
index a7eb960..aacb00e 100644
--- a/services/camera/libcameraservice/api1/CameraClient.h
+++ b/services/camera/libcameraservice/api1/CameraClient.h
@@ -68,7 +68,7 @@
     CameraClient(const sp<CameraService>& cameraService,
             const sp<hardware::ICameraClient>& cameraClient,
             const String16& clientPackageName,
-            const std::unique_ptr<String16>& clientFeatureId,
+            const std::optional<String16>& clientFeatureId,
             int cameraId,
             int cameraFacing,
             int clientPid,