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
diff --git a/src/com/android/launcher3/SecondaryDropTarget.java b/src/com/android/launcher3/SecondaryDropTarget.java
index 1362586..0a4fb73 100644
--- a/src/com/android/launcher3/SecondaryDropTarget.java
+++ b/src/com/android/launcher3/SecondaryDropTarget.java
@@ -362,7 +362,7 @@
 
         public void onLauncherResume() {
             // We use MATCH_UNINSTALLED_PACKAGES as the app can be on SD card as well.
-            if (new PackageManagerHelper(mContext).getApplicationInfo(mPackageName,
+            if (PackageManagerHelper.INSTANCE.get(mContext).getApplicationInfo(mPackageName,
                     mDragObject.dragInfo.user, PackageManager.MATCH_UNINSTALLED_PACKAGES) == null) {
                 mDragObject.dragSource = mOriginal;
                 mOriginal.onDropCompleted(SecondaryDropTarget.this, mDragObject, true);