3469 Reland “[cross_file] Migrate to null-safety. (#3452)” (cla: yes, p: cross_file)

3470 [ci] fix ci failure on ios builds (cla: yes)

3472 [camera] Fix example reference in camera’s doc (cla: yes, p: camera)

3473 [local_auth] Fix incorrect switch fallthrough (cla: yes, p: local_auth)

3475 [url_launcher] Update result to True when the url was loaded successfully. (cla: yes, p: url_launcher, platform-ios)

3476 [url_launcher_web] Fix Link misalignment issue (cla: yes, p: url_launcher)

3478 [package_info] Register IntegrationTestPlugin in the example app. (cla: yes, p: package_info)