Announce SideFPS indicator when it's shown

We intentionally don't want to focus
on the UI element; we only want to inform the
user of why it's showing (to encourage the user
to use side fps to authenticate).

Bug: 344763543
Test: atest SideFpsOverlayViewBinderTest
Flag: EXEMPTY bugfix

Change-Id: I9dce65a20cb7cdcb39f888b8b29c3a48c6d5f7a7