3584 [url_launcher] Update platforms to NNBD stable (cla: yes, nnbd, p: url_launcher, platform-linux, platform-macos, platform-web, platform-windows)

3603 [url_launcher] Bump app-facing version for NNBD stable (cla: yes, nnbd, p: url_launcher)

3650 Update plugin_platform_interface min version (cla: yes, p: battery, p: camera, p: connectivity, p: device_info, p: file_selector, p: google_maps_flutter, p: image_picker, p: path_provider, p: url_launcher, p: wifi_info_flutter)

3657 [url_launcher] Migrate unit tests to NNBD (cla: yes, p: url_launcher)