activity_manager_procstate_aidl: Create library for filegroup.

This is required by cameraservice_test_host. Other filegroups in this
.bp file have associated libraries, but none exists for
activity_manager_procstate_aidl.

Bug: 207411352
Test: Built libactivity_manager_procstate_aidl-cpp.
Change-Id: I24cd93271c83e825166f212e033ec5dbb05d8681

core/java/Android.bp

@@ -301,6 +301,17 @@ cc_library {
     ],
 }
 
+cc_library {
+    name: "libactivity_manager_procstate_aidl-cpp",
+    host_supported: true,
+    srcs: [
+        ":activity_manager_procstate_aidl",
+    ],
+    aidl: {
+        export_aidl_headers: true,
+    },
+}
+
 // Build Rust bindings for PermissionController. Needed by keystore2.
 aidl_interface {
     name: "android.os.permissions_aidl",