3887 [in_app_purchase] update min Flutter version to 1.20.0 (cla: yes, waiting for tree to go green, p: in_app_purchase, platform-ios)

3893 [url_launcher] Migrate pushRouteNameToFramework to ChannelBuffers (cla: yes, waiting for tree to go green, p: url_launcher)

3894 Bump min Android SDK to the version required at runtime (cla: yes, waiting for tree to go green, p: webview_flutter, p: google_maps_flutter, platform-android)

3898 [image_picker] Image picker fix camera device (cla: yes, waiting for tree to go green, p: image_picker, platform-ios)

3901 [espresso] Minor cleanup (cla: yes, waiting for tree to go green, p: espresso)