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/pm/InstallSessionHelper.java

@@ -168,7 +168,7 @@ public class InstallSessionHelper {
         synchronized (mSessionVerifiedMap) {
             if (!mSessionVerifiedMap.containsKey(pkg)) {
                 boolean hasSystemFlag = DEBUG || mAppContext.getPackageName().equals(pkg)
-                        || new PackageManagerHelper(mAppContext)
+                        || PackageManagerHelper.INSTANCE.get(mAppContext)
                                 .getApplicationInfo(pkg, user, ApplicationInfo.FLAG_SYSTEM) != null;
                 mSessionVerifiedMap.put(pkg, hasSystemFlag);
             }
@@ -242,7 +242,7 @@ public class InstallSessionHelper {
                 && sessionInfo.getInstallReason() == PackageManager.INSTALL_REASON_USER
                 && sessionInfo.getAppIcon() != null
                 && !TextUtils.isEmpty(sessionInfo.getAppLabel())
-                && !new PackageManagerHelper(mAppContext).isAppInstalled(
+                && !PackageManagerHelper.INSTANCE.get(mAppContext).isAppInstalled(
                         sessionInfo.getAppPackageName(), getUserHandle(sessionInfo));
     }