Add @UsesReflection to FeatureFactory reflection usage

Ensure FeatureFactory implementations are kept using a @UsesReflection
annotation at the callsite where they are instantiated via reflection.

Bug: 272041779
Test: m + validate FeatureFactoryImpl is kept
Change-Id: Ia9b8c4fd2c438805f33561dcacd5c10ed49dee19
diff --git a/Android.bp b/Android.bp
index fd97dc3..abd3e62 100644
--- a/Android.bp
+++ b/Android.bp
@@ -106,6 +106,7 @@
     plugins: ["androidx.room_room-compiler-plugin"],
 
     libs: [
+        "keepanno-annotations",
         "telephony-common",
         "ims-common",
     ],