Ignore @FlaggedApi annotated API in udc mainline branch

Merged-In since this is a udc-mainline-prod only change.

Test: m
Bug: 299411828
Merged-In: Ib69d2fdc1d73b36a08a3d8ae1f2c45b2bcffae64
Change-Id: I4870fbe882ce0ec995dcaeb8a2624071fee6dce7

framework/Android.bp

@@ -22,6 +22,10 @@ package {
 // In the branch which does not support FlaggedAPI, use this default to ignore the annotated APIs.
 java_defaults {
     name: "FlaggedApiDefaults",
+    api_dir: "udc-extended-api",
+    droiddoc_options: [
+      "--hide-annotation android.annotation.FlaggedApi",
+    ],
 }
 
 // The above variables may have different values