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 0c230cf92f4efbacbd8a20ab7b0b7c6c5f5e92b6)

Exempt-From-Owner-Approval: CP from master
diff --git a/services/camera/libcameraservice/CameraService.h b/services/camera/libcameraservice/CameraService.h
index 1283148..4e04f0e 100644
--- a/services/camera/libcameraservice/CameraService.h
+++ b/services/camera/libcameraservice/CameraService.h
@@ -50,6 +50,7 @@
 #include <string>
 #include <map>
 #include <memory>
+#include <optional>
 #include <utility>
 #include <unordered_map>
 #include <unordered_set>