40161 Add fullscreenDialog argument in PageRouteBuilder

40461 Implement DropdownButton.selectedItemBuilder

41415 Expose API for resizing image caches

42250 SliverAppBar - Configurable overscroll stretch with callback feature & FlexibleSpaceBar support

42485 Re-landing SliverAnimatedList.

42842 Add “navigator” option to “showDialog” and “showGeneralDialog”

43286 FadeInImage cacheWidth and cacheHeight support

44289 SliverOpacity

45127 SliverIgnorePointer

45432 Use RenderSliverPadding to inset SliverFillViewport

iOS support