66980 [flutter_tools] fix documentation, globals, and todos in the android codebase (cla: yes, tool)

66983 [flutter_tools] prevent running analyze-size with split-debug-info (cla: yes, tool)

66985 migrate some material files to nullsafety (cla: yes, f: material design, framework)

66992 Roll Engine from a6a6fd163b99 to 83b9df9df59c (18 revisions) (cla: yes, waiting for tree to go green)

66995 [flutter_tool] enable single widget reload optimization by default on dev (cla: yes, tool, waiting for tree to go green)

66997 Fix Windows and Linux plugin template filenames (cla: yes, tool, waiting for tree to go green)