40390 a11y improvements for textfield (cla: yes, f: material design, framework, waiting for tree to go green)

40391 Place conditional imports on same line (a: tests, cla: yes, framework)

40393 Convert build mode to lowercase in tool_backend (a: desktop, cla: yes, tool)

40394 Roll engine to 6e6de944536b820e4f148036b01004ef0ed68917 (cla: yes, engine)

40397 Adds list required components when VS is not installed (cla: yes, t: flutter doctor, tool, ❖ platform-windows)