72558 Migrate some sample code to NNBD [1] (a: null-safety, cla: yes, d: api docs, d: examples, documentation, framework, team, waiting for tree to go green)

72755 Migrate some sample code to NNBD [2] (a: null-safety, cla: yes, d: api docs, d: examples, documentation, f: cupertino, framework, team, waiting for tree to go green)

72761 Build iOS apps using Swift Packages (cla: yes, d: examples, platform-ios, t: xcode, team, tool)

72829 Migrate some sample code to NNBD [3] (a: null-safety, cla: yes, d: api docs, d: examples, documentation, f: cupertino, framework, team, waiting for tree to go green)