aidl: put @utf8InCpp

String type in AIDL is mapped to String16 in C++, which doesn't work
well with ParcelFileDescriptor. (String16 is not moveable while PFD is
moveable but not copyable.)

Putting @utf8InCpp makes String type in AIDL std::string in C++.
std::string has no such problems.

Besides, there's no good reason to use String16 in C++.

Bug: 192136980
Test: MicrodroidHostTestCases, VirtualizationTestCases
Change-Id: I47ffd5f9083a7bd446fbff6a806f1d31295e6cd3
diff --git a/tests/vsock_test.cc b/tests/vsock_test.cc
index 233c6dd..931e79d 100644
--- a/tests/vsock_test.cc
+++ b/tests/vsock_test.cc
@@ -86,7 +86,7 @@
     VirtualMachineConfig config;
     config.kernel = ParcelFileDescriptor(unique_fd(open(kVmKernelPath, O_RDONLY | O_CLOEXEC)));
     config.initrd = ParcelFileDescriptor(unique_fd(open(kVmInitrdPath, O_RDONLY | O_CLOEXEC)));
-    config.params = String16(kVmParams);
+    config.params = kVmParams;
     config.protected_vm = protected_vm;
 
     sp<IVirtualMachine> vm;