58511 Add material page, cupertino page, and transition page classes (cla: yes, framework)

58514 add rasterizer start times to timeline summaries (a: tests, cla: yes, framework, waiting for tree to go green)

58530 [Line Heights] Add textHeightBehavior to SelectableText. (cla: yes, f: material design, framework, waiting for tree to go green)

58535 Make _RenderSlider not be a semantics container (a: accessibility, cla: yes, f: focus, f: material design, framework)

58593 Add collapsed height param to SliverAppBar (cla: yes, f: material design, framework, waiting for tree to go green)