Make SIM import screen an activity

This fixes an accessibility bug where the toolbar navigation icon was
announced instead of the title when the screen is displayed

test
* manually verify that SIM import works as previously when launched from
  settings and from assistant.
* manually verify that activity label is announced instead of navigation
  icon

Bug 32947074

Change-Id: I1116d626f13842ad78e287c98dd3a051796b1f5f