Make @Discouraged visible to libcore/ and art/

This change adds android.annotation.Discouraged to the list of
API annotations from the framework that can be used in libcore/ and
art/.

Bug: 202993567
Test: Check that importing android.annotation.Discouraged does not
      result in a build error when imported in arbitrary java files in
      libcore.
Change-Id: If8ff4fbd13d403d9bb1f10f7d9f98f5782ba4818
diff --git a/java/Android.bp b/java/Android.bp
index 7a592d6..bcc3349 100644
--- a/java/Android.bp
+++ b/java/Android.bp
@@ -51,6 +51,7 @@
 filegroup {
     name: "framework-api-annotations",
     srcs: [
+        "android/annotation/Discouraged.java",
         "android/annotation/SystemApi.java",
         "android/annotation/TestApi.java",
     ],
@@ -88,4 +89,3 @@
         "//frameworks/base/core/java",
     ],
 }
-