Fix missing Themed Icons and Grid Layout entries on start up

In SUW, Launcher is not yet ready, therefore themed icon status and grid
options cannot be retrieved. Set up retry as part of the themed icon and
grid repository flow, to retry getting themed icons and grid on app
launch. Also convert grid flow to a callback flow using
a content observer so it updates automatically when grid settings is
updated.

Flag: com.android.systemui.shared.new_customization_picker_ui
Test: unit tests still pass
Test: manually verified themed icons & grid show on factory reset
Test: manually verified themed icons & grid set correctly
Bug: 419177073
Change-Id: I3d2f0a1c68426c380f6a9319f3f8d731fd74eae5