3841 [in_app_purchase] Federated Android implementation (cla: yes, p: in_app_purchase, platform-android)

3842 [tool] add an skip-confirmation flag to publish-package for running the command on ci (cla: yes, last mile)

3844 Update third_party license checking (cla: yes)

3845 [in_app_purchase] Add warning in readme for double import of the Android billing client library (cla: yes, p: in_app_purchase)

3846 Move incremental_build.sh to run-on-changed-packages (cla: yes)

3847 Add support for third_party packages in Dart code (cla: yes)

3848 [google_sign_in] remove execute bit from a lot of files (cla: yes, p: google_sign_in, platform-ios, platform-android)