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/AllAppsList.java

@@ -169,7 +169,7 @@ public class AllAppsList {
     public AppInfo addPromiseApp(
             Context context, PackageInstallInfo installInfo, boolean loadIcon) {
         // only if not yet installed
-        if (new PackageManagerHelper(context)
+        if (PackageManagerHelper.INSTANCE.get(context)
                 .isAppInstalled(installInfo.packageName, installInfo.user)) {
             return null;
         }