3140 [file_selector] initial implementation (cla: yes)

3141 [file_selector_web]: Add initial implementation (cla: yes, waiting for test harness)

3142 [url_launcher] Url launcher platform interface null safety (cla: yes)

3143 [wifi_info_flutter] Wifi plugin implementation (cla: yes)

3144 [device_info_platform_interface][device_info] nnbd (cla: yes)

3145 [in_app_purchase] Add example test target to Podfile, add OCMock dependency (cla: yes)

3146 [path_provider] Log errors in the linux example (cla: yes)

3148 [url_launcher] migrate url_launcher package to null safety (cla: yes)

3149 Add windows directory to examples (cla: yes)