Refactor shortcut updating, and do it on BOOT_COMPLETE

This CL shuffles quite a bit of code around, but the effective differences are:
* Unified shortcut updating code (language switch & backup restoration).
* Shortcuts are also updated on boot (flagged by MODES_UI which will need this).
* Removed usage of (long obsolete) AsyncTask.

A further CL will add some special-casing for the DND->Modes shortcut transition.

Bug: 365545604
Test: atest com.android.settings.shortcut + manual (switch language, reboot)
Flag: android.app.modes_ui
Change-Id: I30450d13cb05008d2a71ed89d4781eb81e5532b9

src/com/android/settings/shortcut/ShortcutsUpdateReceiver.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settings.shortcut;
+
+import android.app.Flags;
+import android.content.BroadcastReceiver;
+import android.content.Context;
+import android.content.Intent;
+import android.util.Log;
+
+import androidx.annotation.NonNull;
+
+import com.android.settingslib.utils.ThreadUtils;
+
+public class ShortcutsUpdateReceiver extends BroadcastReceiver {
+
+    private static final String TAG = "ShortcutsUpdateReceiver";
+
+    @Override
+    public void onReceive(@NonNull Context context, @NonNull Intent intent) {
+        if (!Flags.modesApi() || !Flags.modesUi()) {
+            return;
+        }
+
+        if (Intent.ACTION_BOOT_COMPLETED.equals(intent.getAction())) {
+            PendingResult pendingResult = goAsync();
+
+            ThreadUtils.getBackgroundExecutor().execute(() -> {
+                try {
+                    ShortcutsUpdater.updatePinnedShortcuts(context);
+                } catch (Exception e) {
+                    Log.e(TAG, "Error trying to update Settings shortcuts", e);
+                } finally {
+                    pendingResult.finish();
+                }
+            });
+        }
+    }
+}