16935 Improve iOS PlatformViews to better handle thread merging. (cla: yes)

17015 Support EventChannel C++ plugin API for Linux/Windows (cla: yes)

17151 Small updates to objcdocs (cla: yes)

17175 Enhance image_filter_layer caching to filter a cached child (cla: yes, perf: speed, severe: performance, waiting for tree to go green)

17275 [tools][fuchsia] Do not tar debug symbol CIPD uploads (cla: yes)

17304 Add pointer events to the Linux shell (cla: yes)

17305 onRequestPermissionsResult now require calling super on AndroidX master (cla: yes)

17363 Refactor FlutterEngine usage in Linux shell (cla: yes)