65422 [flutter_tools] only lock if an upgrade/download will be performed (linux/macos) and output building messages to stderr (cla: yes, team, tool)

65505 Creates a way to test private APIs in the Flutter package. (cla: yes, framework, team, waiting for tree to go green)

65530 Have the analyzer bot ignore .DS_Store files. (cla: yes, team, waiting for tree to go green)

65568 Remove unused ‘dart:async’ imports. (a: accessibility, a: internationalization, a: tests, cla: yes, f: cupertino, f: material design, framework, team, tool)

65578 Add mac builders to try configurations. (cla: yes, team, waiting for tree to go green)