Better adaptaion of Material Design

[MahMoos]

Disclaimer: you may find some of the changes here opinionated, but I find them necessary to give more flexibility in usage.

• Add path property to AdaptiveScaffoldDestination for simpler usage with routing.
• Add AdaptiveNavigationScaffold.of(context) method to provide its state to descendants.
• Add appBarBuilder to build different AppBars depending on NavigationType.
• Add navigationRailTrailing and permanentDrawerFooter.
• Make the drawer scrollable (closes #35).
• FAB now can be inside permanentDrawer and is controlled by fabInPermanentDrawer property.
• Add railDestinationsOverflow property.
• Add showVerticalDivider to make the VerticalDivider between body and NavigationRail/permanentDrawer optional (closes #56).
• Menu/Back button is now moved inside NavigationRail from the AppBar to be perfectly aligned with NavigationRailDestinations (closes #2).
• Make floatingActionButton type Widget not FloatingActionButton as it is in the Scaffold (closes #44).
• Add AdaptiveFloatingActionButton. This widget should be used to have an expanded FAB inside the permanent drawer.
• Update examples, and use Material 3 theming.
• Update dependencies (close #55).

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[guidezpl]

Thank you for your contribution. I'm really glad you're excited about Flutter! Unfortunately your patch does not currently meet our quality bar because it makes too many unrelated changes, and is missing CHANGELOG entries.

I suggest breaking this up in 2-3 PRs, separating adding functionality from breaking changes like replacing functionality. Please don't hesitate to submit a new PR at https://github.com/material-foundation/flutter-packages if you have the time. Thanks!