[Flexiglass] Add support for the Side FPS indicator in Flexiglass.

Fix: 299343641
Test: Test manually by entering the bouncer scene on a device with side
FPS and observing the indicator is there. Ensured the indicator is not
there when the bouncer is dismissed or on a UDFPS device.
Test: Added unit tests.
Flag: ACONFIG com.android.systemui.scene_container DEVELOPMENT

Change-Id: Ic9622834f08b6f08edaade1dddbf6c728a57609c