Fix empty picker when launcher isn't ready

Grid flow wasn't emitting when PreviewUtils is null, blocking the
isAvailable check, which blocked initializing customization picker. Make
isAvailable flow in grid repository depend directly on PreviewUtils flow
so that isAvailable is always emitted, and always refreshed if
necessary. Also take care of case where picker is launched first in SUW
when Launcher isn't available, then relaunched after finishing SUW, and
make sure shape and grid options appear correctly. This requires
changing shape to observe provider changes instead of getting options
only in init in the Singleton repository.

Flag: com.android.systemui.shared.new_customization_picker_ui
Bug: 423648739
Bug: 421526288
Test: manually verified in and out of SUW
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:84fa39df8500f859d1da12260f880680e3c3f73c)
Merged-In: I31596b2b88e0f2b26d90200f42b354cb0f87db82
Change-Id: I31596b2b88e0f2b26d90200f42b354cb0f87db82