4458 [in_app_purchase] Add support for promotional offers through Store-Kit wrappers (cla: yes, waiting for tree to go green, p: in_app_purchase, platform-ios)

4461 Fix bugs in Dart Implementation of the Pigeon API  (cla: yes, waiting for tree to go green, p: webview_flutter, platform-android)

4468 [ci] Remove unused dep from file_selector. (cla: yes, waiting for tree to go green, p: file_selector, platform-web)

4474 [flutter_plugin_tools] Add ‘main’ support (cla: yes, waiting for tree to go green)

4478 Adjust pull request template (cla: yes, waiting for tree to go green)