67629 enable lint cast_nullable_to_non_nullable (a: tests, cla: yes, f: cupertino, f: material design, framework)

67652 Replace the flag emoji in the emoji caret test with a modifier sequence (cla: yes, framework, waiting for tree to go green)

67654 [flutter_tools] always run build tests on presubmit (cla: yes, team)

67656 Fix new analyzer rule failure (cla: yes, f: material design, framework)

67668 fix the tree (cla: yes, f: material design, framework)

67669 [flutter_tools] fold executable resolution into flutter (cla: yes, tool)

67670 Replace MockUsage with Usage.test in build tests (cla: yes, team, tool)