Resuming install if user trusted the source

Intenting to the app specific page. The code for partners already
allows PackageInstallerActivity to resume the install if RESULT_OK was
set before the settings activity was finished.

Test: Manually tested that the install resumes if the user trusted the
source

Bug: 35487166

Change-Id: I47131b326765b7fc8eb74dc922595234a49d0153