Expose Intent#ACTION_CLEAR_DNS_CACHE

DnsManager will broadcast ACTION_CLEAR_DNS_CACHE intent to clear
dns cache when network have changed. But DnsManager is in the
Connectivity mainline module which can not use non-formal API.
Thus, expose Intent#ACTION_CLEAR_DNS_CACHE as module lib API for
mainline module.

Bug: 182370679
Test: m update-api
Change-Id: I30b1b146dcae82926be7bdb8b343635a01eabefe

core/api/module-lib-current.txt

@@ -59,6 +59,10 @@ package android.content {
     method @NonNull public android.os.UserHandle getUser();
   }
 
+  public class Intent implements java.lang.Cloneable android.os.Parcelable {
+    field public static final String ACTION_CLEAR_DNS_CACHE = "android.intent.action.CLEAR_DNS_CACHE";
+  }
+
 }
 
 package android.content.pm {

core/java/android/content/Intent.java

@@ -2331,6 +2331,7 @@ public class Intent implements Parcelable, Cloneable {
      * @hide
      */
     @SdkConstant(SdkConstantType.BROADCAST_INTENT_ACTION)
+    @SystemApi(client = SystemApi.Client.MODULE_LIBRARIES)
     public static final String ACTION_CLEAR_DNS_CACHE = "android.intent.action.CLEAR_DNS_CACHE";
     /**
      * Alarm Changed Action: This is broadcast when the AlarmClock