Support installation of the new app source certificate

The new certificate can be installed from Settings ("Install a
certificate > App Source certificate").  The installation flow includes
a warning with user authorization to proceed, then a prompt for reboot
(now or later).

Installed certificate can be managed in "User credentials".  The name is
currently a hash of hex numbers.

Upon deletion, there will also be a promot for reboot (now or later).

Test: Only see the new setting entry if feature is enabled
Test: Install from Settings, see the expected file name in
      /data/misc/keysetore/user_0.  Reboot also works.
Test: Able to see the certificate in Settings after installed
Test: Able to delete the certificate, which triggers confirmation dialog
      to reboot.  Reboot works.
Test: add certificate, see dialog, "not now" / tapping elsewhere does
      nothing
Test: atest RestrictedEncryptionPreferenceControllerTest
Bug: 112038744

Change-Id: I7a4494ea0f243730df2212076588074d8774ae23
diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index 3f66cb8..0ba07c3 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -1313,6 +1313,11 @@
                   android:exported="false">
         </activity>
 
+        <activity android:name=".security.InstallAppSourceCertificateWarning"
+                  android:theme="@style/GlifV3Theme.Light"
+                  android:exported="false">
+        </activity>
+
         <activity
             android:name="Settings$DeviceAdminSettingsActivity"
             android:label="@string/device_admin_settings_title">