Updater: use Build.getSerial() instead of direct ro.serialno read

platform_app cannot access serialno_prop (AOSP neverallow). Route
through Build.getSerial() which delegates to DeviceIdentifiersPolicyService
in system_server. Add READ_PRIVILEGED_PHONE_STATE to manifest and
privapp-permissions allowlist.

app/me.pawlet.updater.xml

@@ -6,6 +6,7 @@
 <permissions>
     <privapp-permissions package="me.pawlet.updater">
         <permission name="android.permission.ACCESS_CACHE_FILESYSTEM"/>
+        <permission name="android.permission.READ_PRIVILEGED_PHONE_STATE"/>
         <permission name="android.permission.REBOOT"/>
         <permission name="android.permission.RECOVERY"/>
         <permission name="android.permission.START_ACTIVITIES_FROM_BACKGROUND"/>

app/src/main/AndroidManifest.xml

@@ -17,6 +17,7 @@
     <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
     <uses-permission android:name="android.permission.RECOVERY" />
     <uses-permission android:name="android.permission.START_ACTIVITIES_FROM_BACKGROUND" />
+    <uses-permission android:name="android.permission.READ_PRIVILEGED_PHONE_STATE" />
     <uses-permission android:name="android.permission.WAKE_LOCK" />
 
     <application

app/src/main/java/me/pawlet/updater/misc/Utils.java

@@ -14,6 +14,7 @@ import android.content.pm.PackageManager;
 import android.net.ConnectivityManager;
 import android.net.Network;
 import android.net.NetworkCapabilities;
+import android.os.Build;
 import android.os.SystemProperties;
 import android.os.storage.StorageManager;
 import android.util.Log;
@@ -155,7 +156,7 @@ public class Utils {
         String device = SystemProperties.get(Constants.PROP_NEXT_DEVICE,
                 SystemProperties.get(Constants.PROP_DEVICE));
         String type = SystemProperties.get(Constants.PROP_RELEASE_TYPE).toLowerCase(Locale.ROOT);
-        String serial = SystemProperties.get("ro.serialno", "");
+        String serial = Build.getSerial().equals(Build.UNKNOWN) ? "" : Build.getSerial();
 
         String serverUrl = SystemProperties.get(Constants.PROP_UPDATER_URI);
         if (serverUrl.trim().isEmpty()) {
@@ -177,7 +178,7 @@ public class Utils {
     public static String getChangelogURL(Context context) {
         String device = SystemProperties.get(Constants.PROP_NEXT_DEVICE,
                 SystemProperties.get(Constants.PROP_DEVICE));
-        String serial = SystemProperties.get("ro.serialno", "");
+        String serial = Build.getSerial().equals(Build.UNKNOWN) ? "" : Build.getSerial();
         return context.getString(R.string.menu_changelog_url)
                 .replace("{device}", device)
                 .replace("{sn}", serial);