Migrate PackageManagerHelper to MainThreadInitializedObject

- This is in preparation for other things that can be loaded with
  PMH initialization and prevents duplicate temporary helpers from
  loading this many times.
- Most calls in PMH can use the app context, but one call requires
  starting activities/showing toasts so that one needs to take the
  context and can be made static instead.

Bug: 323112914
Test: atest NexusLauncherTests
Change-Id: Id11c780955880cf49c022cbf2744c41e1b696355

src/com/android/launcher3/model/SdCardAvailableReceiver.java

@@ -52,7 +52,7 @@ public class SdCardAvailableReceiver extends BroadcastReceiver {
     @Override
     public void onReceive(Context context, Intent intent) {
         final LauncherApps launcherApps = context.getSystemService(LauncherApps.class);
-        final PackageManagerHelper pmHelper = new PackageManagerHelper(context);
+        final PackageManagerHelper pmHelper = PackageManagerHelper.INSTANCE.get(context);
         for (PackageUserKey puk : mPackages) {
             UserHandle user = puk.mUser;