Add a temporary activity-alias for TunerActivity.

Bug: 31781480
Test: make SystemUI, and manually inspected sysui appears in
Settings. Turning off sysui tuner still works.

The new alias is used by Settings to display sysui tuner in a different
category instead of in homepage directly. The display location is
controlled by category metadata. We need a alias because the category
metadata is different between new/old activity.

Change-Id: Ie4f2c1f6017459e34227155c83a7767f2003b18b