Add aconfig declarations to f/b droidstubs

This change pass the aconfig_declaration modules defined in
AconfigFlags.bp to the *-api-stubs-docs-non-updatable droidstubs module,
so that the "exportable" stubs (i.e. the stubs only containing the
flagged apis that are enabled by the release configuration) can be
generated.

Test: m api-stubs-docs-non-updatable && m checkapi
Bug: 317290555
Change-Id: I944d336e474b9ed61f4554fc9325a8df3a9cf40b
diff --git a/api/Android.bp b/api/Android.bp
index 1686943..126176d 100644
--- a/api/Android.bp
+++ b/api/Android.bp
@@ -269,6 +269,7 @@
 // classpath (or sources) somehow.
 stubs_defaults {
     name: "android-non-updatable-stubs-defaults",
+    defaults: ["framework-minus-apex-aconfig-declarations"],
     srcs: [":android-non-updatable-stub-sources"],
     sdk_version: "none",
     system_modules: "none",