83423 Revert “[flutter_tools] Make flutter upgrade only work with standard remotes” (tool, cla: yes)

83433 fix lint from an improved unnecessary_parenthesis (team, tool, framework, cla: yes, waiting for tree to go green)

83437 Fix benchmark regression from #83427 (tool, cla: yes, waiting for tree to go green)

83441 Migrate pubspec_schema to null safety (tool, cla: yes, waiting for tree to go green, a: null-safety)

83442 Clean up null assumptions for Xcode and CocoaPods classes (tool, cla: yes, waiting for tree to go green, a: null-safety)

83443 Clean up null assumptions for Gradle classes (tool, cla: yes, waiting for tree to go green, a: null-safety)