Use std::optional for @nullable (AIDL)

Previously, nullable types were mapped to std::unique_ptr for C++
backend. But std::unique_ptr typically involves unnecessary alloc/dealloc.

For example, if nullable string is represented in unique_ptr<string>, we
should do "unique_ptr<string>(new string(value))" to set a value.

To avoid breaking all hand-written parcelables, only new read/write
functions are added to Parcel class and they are used only by
aidl-generated code and their implementations.

Bug: 144773267
Test: build/flash/boot
      atest --test-mapping frameworks/native/libs/binder

Merged-In: I2c801e3b69f2f8ccf44267f15cbf79e1d8fbf19e
Change-Id: I2c801e3b69f2f8ccf44267f15cbf79e1d8fbf19e
(cherry picked from commit 1e1c5fbbbe8a76150fe832c8f974cbd543aa0860)

Exempt-From-Owner-Approval: CP from master
diff --git a/libs/binder/IAppOpsService.cpp b/libs/binder/IAppOpsService.cpp
index b2bd9e5..e5f0a11 100644
--- a/libs/binder/IAppOpsService.cpp
+++ b/libs/binder/IAppOpsService.cpp
@@ -22,6 +22,8 @@
 #include <binder/Parcel.h>
 #include <utils/String8.h>
 
+#include <optional>
+
 namespace android {
 
 // ----------------------------------------------------------------------