Add explicit android:exported="true" declarations

We add this for GestureSandboxActivity and
com.android.launcher3.uioverrides.QuickstepLauncher to
reinstate the behavior of go/ag/11746107 which was
incorrectly reverted in go/ag/11963698.

We also add this for HotseatEduActivity which was
newly added in go/ag/11963698.

(Cherry pick from master cadb94983be5ab558202041a053eb4b67ccf3c01)

Bug: 159709775
Fixes: 159709775
Test: wembley-userdebug boots and has functioning Launcher
Change-Id: I17904f9ad88abc66364675426545eae423cb3175
Merged-In: I17904f9ad88abc66364675426545eae423cb3175
diff --git a/quickstep/AndroidManifest.xml b/quickstep/AndroidManifest.xml
index a4b1966..4e7c3fa 100644
--- a/quickstep/AndroidManifest.xml
+++ b/quickstep/AndroidManifest.xml
@@ -110,7 +110,8 @@
             android:noHistory="true"
             android:launchMode="singleTask"
             android:clearTaskOnLaunch="true"
-            android:permission="${packageName}.permission.HOTSEAT_EDU">
+            android:permission="${packageName}.permission.HOTSEAT_EDU"
+            android:exported="true">
             <intent-filter>
                 <action android:name="com.android.launcher3.action.SHOW_HYBRID_HOTSEAT_EDU"/>
                 <category android:name="android.intent.category.DEFAULT" />