[Work profile] Fix flickering work mode switch

Since there is no system broadcast with Intent.ACTION_MANAGED_PROFILE_ADDED, UserCache's user list does not get updated when a new profile is installed until launcher is restarted. This change fixes that problem by getting the freshest list of users directly from UserManager.

This change also applies the proper padding to work apps recycler-view after work mode switch is attached.

Test: Manual
Bug: 201191227
Change-Id: I0f570eba44ebb845d0d6f8c5f14a63f9a8c18539