77386 Roll Engine from 299eb3e710c1 to 67abe7f9a9e4 (13 revisions) (a: tests, cla: yes, engine, framework)

77390 [flutter_tools] replace MockFlutterVersion usage with fake where possible, move from context (cla: yes, tool, waiting for tree to go green)

77398 enable prefer_function_declarations_over_variables lint (a: accessibility, a: tests, cla: yes, f: cupertino, f: material design, framework, team, tool, waiting for tree to go green)

77399 [flutter_tools] add tool feature/scaffold for UWP (cla: yes, tool, waiting for tree to go green)

77400 [flutter_tools] migrate to null safe mustache (cla: yes, team, waiting for tree to go green)