AdbDebuggingManager: Add @Keep to mPublicKey.

This field is accessed via reflection, so make sure to not optimize
it out at compile-time.

Bug: 348040664
Test: Manual. Test adb wireless debugging (pairing/connect).
Flag: EXEMPT bugfix

Change-Id: I59befbe99cc7cf797eafc55a939692bfcb5abfef
diff --git a/services/core/java/com/android/server/adb/AdbDebuggingManager.java b/services/core/java/com/android/server/adb/AdbDebuggingManager.java
index 34c3d7e..a73a991 100644
--- a/services/core/java/com/android/server/adb/AdbDebuggingManager.java
+++ b/services/core/java/com/android/server/adb/AdbDebuggingManager.java
@@ -74,6 +74,7 @@
 import android.util.Xml;
 
 import com.android.internal.R;
+import com.android.internal.annotations.Keep;
 import com.android.internal.annotations.VisibleForTesting;
 import com.android.internal.messages.nano.SystemMessageProto.SystemMessage;
 import com.android.internal.util.FrameworkStatsLog;
@@ -214,7 +215,7 @@
 
     class PairingThread extends Thread implements NsdManager.RegistrationListener {
         private NsdManager mNsdManager;
-        private String mPublicKey;
+        @Keep private String mPublicKey;
         private String mPairingCode;
         private String mGuid;
         private String mServiceName;