26761 Initialize EventChannel state (cla: yes)

26763 Roll Dart SDK from e0ea160bb165 to 7f1d45fab187 (1 revision) (cla: yes, waiting for tree to go green)

26765 Migrate spirv to nnbd (cla: yes, waiting for tree to go green)

26768 Roll Skia from b5b7c982958d to 237bf5284da1 (24 revisions) (cla: yes, waiting for tree to go green)

26769 Fix JSON map type declaration for SystemChrome.setApplicationSwitcherDescription arguments (cla: yes, waiting for tree to go green, platform-web)