Return list of one default option when shape not enabled (1/2)

This is to return a list of one default option (circle) if the shape
cutstomization flag is not turned on.

It resolves the issue that the selected shape option never emits.

Test: Manually tested
Fixes: 388299893
Flag: com.android.systemui.shared.new_customization_picker_ui
Change-Id: I328efa370c1a741e8461dd9b37e37c138eb7e09f