getStagedApexInfo() returns @nullable

Its return value (StagedApexInfo) is nullable, but not in .aidl file.
This doesn't affect in the Java backend, but it matters in the other
native backends including Rust.

Bug: 199146189
Test: m
Change-Id: Idab01ad1989100293e03cd7c2c605eb2d51f2e88
diff --git a/libs/binder/aidl/android/content/pm/IPackageManagerNative.aidl b/libs/binder/aidl/android/content/pm/IPackageManagerNative.aidl
index c076be7..c469ec6 100644
--- a/libs/binder/aidl/android/content/pm/IPackageManagerNative.aidl
+++ b/libs/binder/aidl/android/content/pm/IPackageManagerNative.aidl
@@ -122,5 +122,5 @@
      * Get information of APEX which is staged ready for installation.
      * Returns null if no such APEX is found.
      */
-    StagedApexInfo getStagedApexInfo(in @utf8InCpp String moduleName);
+    @nullable StagedApexInfo getStagedApexInfo(in @utf8InCpp String moduleName);
 }