13270 Add recipe changelog (cla: yes)

13272 [web] [test] Adding firefox install functionality to the test platform (affects: tests, cla: yes, platform-web)

13273 Make flutter_tester support multithreaded testing, and run all Dart tests in both single and multithreaded configurations (cla: yes)

13274 Fix decode feature detection in HtmlCodec (cla: yes)

13275 Flesh out the CanvasKit backend some more (cla: yes)

13280 Android embedding API updates for plugin ecosystem (cla: yes)

13282 Manual Roll of Dart from a61c775db8…e1c409792c (cla: yes)