[flexiglass] Adds more to the Dumpable

As it turns out, SceneContainerStartable was already emitting some stuff
to the dump. This CL adds a bit more.

Next: table logging.

Bug: 392185268
Test: adb shell dumpsys activity service com.android.systemui/.SystemUIService SceneContainerStartable
Test: ran the above command when flexi was enabled and also disabled
sample output is available at https://paste.googleplex.com/6236424177975296
Flag: com.android.systemui.scene_container

Change-Id: I2dbf48c9c2af66a9b4b869c95d2e725f213518a6