75804 [flutter_releases] Flutter Framework 1.26.0-17.5.pre Beta Cherrypicks (cla: yes, engine, f: material design, framework, tool)

75809 Apply bottom margin to FABs that have been boosted into the Safe Area (a: fidelity, a: quality, cla: yes, f: material design, framework, waiting for tree to go green)

75811 Move ensureVisualUpdate call to call sites in WidgetsBinding.attachRootWidget() (cla: yes, framework)

75813 Audit and update deprecation warnings (a: accessibility, cla: yes, f: material design, framework, team, waiting for tree to go green)

75820 Remove some `dynamic’s. (cla: yes, framework, waiting for tree to go green)