Split android-non-updatable-stubs-defaults in two

Put the module classpath defaults into a separate defaults module,
such that users can choose to add the module symbols in a different
way.

Update all the current users to apply both defaults.

Test: m nothing
Change-Id: I22f9518c2e205bfa8ad8d4b630ec976921786b73
diff --git a/ApiDocs.bp b/ApiDocs.bp
index ec7b194..27e1def 100644
--- a/ApiDocs.bp
+++ b/ApiDocs.bp
@@ -57,7 +57,10 @@
 
 stubs_defaults {
     name: "android-non-updatable-doc-stubs-defaults",
-    defaults: ["android-non-updatable-stubs-defaults"],
+    defaults: [
+        "android-non-updatable-stubs-defaults",
+        "module-classpath-stubs-defaults",
+    ],
     srcs: [
         // No longer part of the stubs, but are included in the docs.
         ":android-test-base-sources",