72410 Remove unused dart:async imports. (cla: yes, f: cupertino, framework, tool, waiting for tree to go green)

72431 Fixes: “FloatingActionButton.extended’s isExtended property if false should show icon, not label” (cla: yes, f: material design, framework)

72438 Revert “let NOTICES be double gzip wrapped to reduce on-disk installed space” (cla: yes, framework, team, tool)

72446 Enable structured errors by default. (cla: yes, framework)

72472 Added backwardsCompatibility flag to AppBarTheme (cla: yes, f: material design, framework, waiting for tree to go green)

72476 Allow nullable tweens in TweenAnimationBuilder (a: animation, a: null-safety, cla: yes, framework, waiting for tree to go green)