34738 Update Xcode projects to recommended Xcode 10 project settings (cla: yes, t: xcode, team, waiting for tree to go green)

34739 Disable widgets and material web tests (cla: yes, team)

34750 Revert “Check whether FLUTTER_ROOT and FLUTTER_ROOT/bin are writable.” (cla: yes)

34753 Revert “Add basic desktop linux checks” (cla: yes)

34754 Move hacky flag to common (cla: yes)

34755 Add linux doctor implementation (cla: yes, t: flutter doctor, tool)

34757 Backup docs to GCS (cla: yes)

34758 Added some Widgets of the Week Videos to documentation (cla: yes, d: api docs, framework)