Cache the staged session id to skip a staging again

On restarting install after the user grants install permission to
unknown app, we need to skip staging the original file once again. As
such, pass the stagedsessionId while restarting the activity so that
staging can be skipped.

Bug: 182205982
Test: builds successfully
Test: No CTS Tests. Flag to use new app is turned off by default

Change-Id: Iee72576d535613e39e132ffd9e1a1a452838fb82
diff --git a/packages/PackageInstaller/AndroidManifest.xml b/packages/PackageInstaller/AndroidManifest.xml
index 0d1c9b0..410c4ce 100644
--- a/packages/PackageInstaller/AndroidManifest.xml
+++ b/packages/PackageInstaller/AndroidManifest.xml
@@ -54,7 +54,7 @@
         <activity android:name=".v2.ui.InstallLaunch"
             android:configChanges="orientation|keyboardHidden|screenSize"
             android:theme="@style/Theme.AlertDialogActivity"
-            android:exported="true"/>
+            android:exported="false"/>
 
         <activity android:name=".InstallStart"
                 android:theme="@style/Theme.AlertDialogActivity"