Add activity options flag to force launching an activity in a new task

- This is to work around issues where the caller (ie. RemoteViews) is
  launching a provided pending intent that is immutable and still needs
  to ensure that it is launched in a separate task.

Bug: 112508020
Test: Launch an immutable pending intent from a widget and ensure it
      launches in a new task as expected

Change-Id: I70c318674da15a78418548ee719cb1257f899ac6