79682 Migrate doctor_validator to null safety (a: null-safety, cla: yes, team, tool, waiting for tree to go green)

79795 Update dartdoc to 0.42.0 (cla: yes, team, waiting for tree to go green)

79801 Migrate tools chrome.dart to null safety (a: null-safety, cla: yes, team, tool)

79804 Migrate linux_doctor to null safety (a: null-safety, cla: yes, team, tool)

79805 Migrate vscode to null safety (a: null-safety, cla: yes, team, tool)

79806 Migrate android_workflow to null safety (a: null-safety, cla: yes, team, tool)