67083 [flutter] Update some tests in flutter/test (a: tests, cla: yes, f: material design, framework, waiting for tree to go green)

67105 [AppBarTheme] adds titleSpacing parameter (cla: yes, f: material design, framework)

67135 Expose the tileColor property (cla: yes, f: material design, framework, waiting for tree to go green)

67159 Invalid dates when switching back to calendar mode in the date range picker (cla: yes, f: material design, framework)

67166 migrate material to nullsafety (a: tests, cla: yes, f: cupertino, f: material design, framework, waiting for tree to go green)

67167 Add missing margin to SnackBarAction (cla: yes, f: material design, framework, waiting for tree to go green)