71838 showDialog assertion for non-null builder or child property (cla: yes, f: material design, framework, waiting for tree to go green)

71843 Improve the ScrollBar behavior when nested (a: quality, cla: yes, f: cupertino, f: material design, f: scrolling, framework, severe: new feature, waiting for tree to go green)

71852 Fix text direction logic for material icon variants (cla: yes, f: material design, framework, team, waiting for tree to go green)

71853 Add previews for CupertinoIcons (cla: yes, f: cupertino, f: material design, framework, team, waiting for tree to go green)

71861 Remove isMaterialAppTheme property (cla: yes, f: material design, framework, waiting for tree to go green)

71868 Doc fixes for dry layout (cla: yes, framework)