3548 [google_maps_flutter] Migrate to NNBD (cla: yes, nnbd, p: google_maps_flutter)

3550 [file_selector_web] Migrated to null-safety (cla: yes, nnbd, p: file_selector, platform-web)

3555 [in_app_purchase]  Migrate to NNBD (cla: yes, nnbd, p: in_app_purchase, platform-ios)

3557 [url_launcher] Re-endorse null-safe web implementation. (cla: yes, nnbd, p: url_launcher)

3559 [path_provider] Migrate examples to null-safety (cla: yes, nnbd, p: path_provider, platform-linux, platform-macos, platform-windows)