64020 [flutter_tool] Fix amberctl host address (cla: yes, d: examples, team, tool, waiting for tree to go green)

64021 Use real flutter root for finding pub in command integration test (a: tests, cla: yes, tool)

64046 Revert “fix wrap intrinsic height calculation” (cla: yes, framework)

64050 1.21.0-9.1.pre cherrypicks (cla: yes, engine, f: material design, framework, team, tool)

64055 migrate semantics to nullsafety (a: accessibility, cla: yes, framework, waiting for tree to go green)

64056 Incorrect path.join usage might be causing Windows test failures (cla: yes, team, waiting for tree to go green)