Use optional for nullable types

AIDL generates optional<T> for nullable T types for C++, which is more
efficient and idomatic and easy to use.

Bug: 144773267
Test: build/flash/boot
Merged-In: I90cf2ce1193c479179687d71a5c1416f6cdf0b16
Change-Id: I90cf2ce1193c479179687d71a5c1416f6cdf0b16
(cherry picked from commit 53be7f4db497a05256407bd4c499a8fafc8e095d)

Exempt-From-Owner-Approval: CP from master
diff --git a/services/incremental/IncrementalService.cpp b/services/incremental/IncrementalService.cpp
index 980ae08..9ab1e32 100644
--- a/services/incremental/IncrementalService.cpp
+++ b/services/incremental/IncrementalService.cpp
@@ -1078,7 +1078,7 @@
         return false;
     }
     FileSystemControlParcel fsControlParcel;
-    fsControlParcel.incremental = std::make_unique<IncrementalFileSystemControlParcel>();
+    fsControlParcel.incremental = IncrementalFileSystemControlParcel();
     fsControlParcel.incremental->cmd.reset(base::unique_fd(::dup(ifs.control.cmd)));
     fsControlParcel.incremental->pendingReads.reset(
             base::unique_fd(::dup(ifs.control.pendingReads)));