Add request manage credentials to Settings

Background
* This is part of the work to support
  a credential management app on
  unmanaged devices.

Changes
* Add new activity to Settings to display
  a screen to the user requesting whether
  the calling app can manage their
  KeyChain credentials.
* Display the authentication policy

Manual Testing
* Verify screen is not displayed if intent
  action is not android.security.MANAGE_CREDENTIALS
* Verify screen is not displayed if authentication
  policy is not valid
* Verify button panel is visible if all items in the
  authentication policy are displayed
* Verify button panel is not visible if not all items
  in the authentication policy are displayed. Verify
  that scrolling to the bottom of the item list, the
  button panel becomes visible.

Bug: 165641221
Test: Manual testing
      make RunSettingsRoboTests -j ROBOTEST_FILTER=com.android.settings.security.RequestManageCredentialsTest
Change-Id: Ie23b226f1a285b3de6ec3e91b8880d9144bb24a3