42475 Fix semantics testing now that dropdown can take a11y focus again. (a: accessibility, cla: yes, team)

42476 Refactor BuildMode into class, add jit_release configuration (cla: yes, tool)

42478 Revert “Rewrite MouseTracker’s tracking and notifying algorithm” (cla: yes, framework)

42479 Make DropdownButton’s disabledHint and hint behavior consistent (cla: yes, f: material design, framework, severe: API break)

42482 Only dismiss dropdowns if the orientation changes, not the size. (cla: yes, f: material design, framework)

42484 Gradient transform (cla: yes, framework, will affect goldens)

42485 Re-landing SliverAnimatedList (a: animation, cla: yes, f: scrolling, framework, severe: new feature, waiting for tree to go green)