Add default_visibility for soong modules

So that we don't get surprise usages.

Bug: 348717861
Test: m nothing
Change-Id: I47319a727092c1bd936cca88f5713ee977a48b48
diff --git a/cmd/extract_apks/bundle_proto/Android.bp b/cmd/extract_apks/bundle_proto/Android.bp
index e56c0fb..0abf1e2 100644
--- a/cmd/extract_apks/bundle_proto/Android.bp
+++ b/cmd/extract_apks/bundle_proto/Android.bp
@@ -10,4 +10,8 @@
     proto: {
         canonical_path_from_root: false,
     },
+    visibility: [
+        "//build/soong:__subpackages__",
+        "//tools/mainline:__subpackages__",
+    ],
 }