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
Merged-In: I9045bc6fc2eb06839203af6db94a80de9b83ad1f
Change-Id: I9045bc6fc2eb06839203af6db94a80de9b83ad1f
(cherry picked from commit 3f9a3b407aeff0311038b2097d657446c4f98b90)

Exempt-From-Owner-Approval: CP from master
diff --git a/services/camera/libcameraservice/common/Camera2ClientBase.h b/services/camera/libcameraservice/common/Camera2ClientBase.h
index 042f5aa..d7506af 100644
--- a/services/camera/libcameraservice/common/Camera2ClientBase.h
+++ b/services/camera/libcameraservice/common/Camera2ClientBase.h
@@ -48,7 +48,7 @@
     Camera2ClientBase(const sp<CameraService>& cameraService,
                       const sp<TCamCallbacks>& remoteCallback,
                       const String16& clientPackageName,
-                      const std::unique_ptr<String16>& clientFeatureId,
+                      const std::optional<String16>& clientFeatureId,
                       const String8& cameraId,
                       int api1CameraId,
                       int cameraFacing,