[Navigation Material] Update Navigation Material after ModalBottomSheetLayout bug fixes

[jossiwolf]

This PR refactors our Navigation Material code after upstream updates to ModalBottomSheetLayout that address one-frame consistency and anchor update + reconciliation logic.

We now retain the back stack entry until all animations are completed.

API Changes

API	Status
public ctor BottomSheetNavigatorSheetState	internal ctor
BottomSheetNavigatorSheetState#offset	Deprecated
BottomSheetNavigatorSheetState#direction	Deprecated
BottomSheetNavigatorSheetState#progress	Deprecated

Other changes

• BottomSheetNavigator now uses moveable content under the hood
• The strategy for retaining bottom sheet back stack entries has changed to only dispose of them after the sheet has been hidden

Fixes: #772, #813, #910, #937, #1031, #1147, #1356

[jossiwolf]

@jbw0033 testSheetShownAfterNavControllerRestoresState also seems to fail now - looks like the sheet state doesn't get moved to Hidden. Do you have an idea?