[Vendor] Add filegrouop for NonNull.java

This is needed by google.camera.experimental docs.

Test: m -j docs
Bug: b/70351683

Change-Id: I79b3f0946a1d606cda770eabe7c287f4cc207bfc
diff --git a/Android.bp b/Android.bp
index f11341e..ec80778 100644
--- a/Android.bp
+++ b/Android.bp
@@ -1561,3 +1561,10 @@
         },
     },
 }
+
+filegroup {
+    name: "framework-annotation-nonnull-srcs",
+    srcs: [
+        "core/java/android/annotation/NonNull.java",
+    ],
+}