Include androidx stubs in framework docs

This will allow javadoc links to androidx packages to resolve.

Test: No behavior changes
Bug: 144042891
Change-Id: I01c1cd637f46c666c28669c1796a1d5a0d249c24
diff --git a/Android.bp b/Android.bp
index 543e656..0da799b 100644
--- a/Android.bp
+++ b/Android.bp
@@ -897,7 +897,10 @@
     "-overview $(location core/java/overview.html) " +
     // Federate Support Library references against local API file.
     "-federate SupportLib https://developer.android.com " +
-    "-federationapi SupportLib $(location :current-support-api) "
+    "-federationapi SupportLib $(location :current-support-api) " +
+    // Federate Support Library references against local API file.
+    "-federate AndroidX https://developer.android.com " +
+    "-federationapi AndroidX $(location :current-androidx-api) "
 
 framework_docs_only_libs = [
     "voip-common",
@@ -1015,6 +1018,7 @@
         "core/res/AndroidManifest.xml",
         "core/java/overview.html",
         ":current-support-api",
+        ":current-androidx-api",
     ],
     create_stubs: false,
 }