Generalize @Keep annotation Proguard rules

Consolidate the Proguard rules for @Keep annotations for:
  * android.support.annotation.Keep (existing)
  * androidx.annotation.Keep (existing)
  * com.android.internal.annotation.Keep (new)

This ensures consistent semantics for clients using these annotations
across the codebase. Ideally there would be a single annotation, but
the support libraries are not available everywhere. In practice, this
change should be a no-op.

Bug: 210510433
Test: m + validate identical artifact sizes
Change-Id: Iab494e03269e5758d7f860331e971826ecc08cdd

core/proguard.flags

@@ -15,35 +15,24 @@
 @**.VisibleForTesting *;
 }
 
-# Understand the @Keep support annotation.
--keep class android.support.annotation.Keep
--keep class androidx.annotation.Keep
+# Understand the common @Keep annotation from various Android packages:
+#  * android.support.annotation
+#  * androidx.annotation
+#  * com.android.internal.annotations
+-keep class **android**.annotation*.Keep
 
--keep @android.support.annotation.Keep class * {*;}
--keep @androidx.annotation.Keep class * {*;}
+-keep @**android**.annotation*.Keep class * { *; }
 
 -keepclasseswithmembers class * {
-    @android.support.annotation.Keep <methods>;
+    @**android**.annotation*.Keep <methods>;
 }
 
 -keepclasseswithmembers class * {
-    @androidx.annotation.Keep <methods>;
+    @**android**.annotation*.Keep <fields>;
 }
 
 -keepclasseswithmembers class * {
-    @android.support.annotation.Keep <fields>;
-}
-
--keepclasseswithmembers class * {
-    @androidx.annotation.Keep <fields>;
-}
-
--keepclasseswithmembers class * {
-    @android.support.annotation.Keep <init>(...);
-}
-
--keepclasseswithmembers class * {
-    @androidx.annotation.Keep <init>(...);
+    @**android**.annotation*.Keep <init>(...);
 }
 
 -include proguard_basic_keeps.flags