Whitelist the staging directory in installd

Make the path /data/pkg_staging a valid path for APK and APEX files, inorder
to allow the deletion of APEX files after their corresponding sessions
reach a final state.

Bug: 123624108
Test: manual - trigger APEX deletion from the mentioned directory
Change-Id: I9bf03c924080e8c75a6c0e9d163460d365061487
diff --git a/cmds/installd/utils.cpp b/cmds/installd/utils.cpp
index 5b487bb..f245272 100644
--- a/cmds/installd/utils.cpp
+++ b/cmds/installd/utils.cpp
@@ -892,6 +892,8 @@
 static int validate_apk_path_internal(const std::string& path, int maxSubdirs) {
     if (validate_path(android_app_dir, path, maxSubdirs) == 0) {
         return 0;
+    } else if (validate_path(android_staging_dir, path, maxSubdirs) == 0) {
+        return 0;
     } else if (validate_path(android_app_private_dir, path, maxSubdirs) == 0) {
         return 0;
     } else if (validate_path(android_app_ephemeral_dir, path, maxSubdirs) == 0) {