74866 Add fixes for nullOk changes (a: null-safety, cla: yes, cp: 1.26, cp: 1.26 completed, f: cupertino, f: material design, framework, team, waiting for tree to go green)

74880 Fix a slider layout bug when the overlay size is smaller than the thumb size (cla: yes, f: material design, framework, waiting for tree to go green)

74899 Remove “unnecessary” imports in material/ (cla: yes, f: material design, framework, waiting for tree to go green)

74901 Remove “unnecessary” imports in test/animation (cla: yes, framework, waiting for tree to go green)

74906 Improve Dropdown Menu (cla: yes, f: material design, framework, waiting for tree to go green)