3497 [camera_platform_interface] Migrate to null safety (cla: yes, nnbd, p: camera)

3498 [path_provider] Update macOS for NNBD (cla: yes, nnbd, p: path_provider, platform-macos)

3499 [android_alarm_manager] Migrated android_alarm_manager to support null safety #75233 (cla: yes, nnbd, p: android_alarm_manager)

3505 [shared_preferences] Update macOS for NNBD (cla: yes, nnbd, p: shared_preferences, platform-macos)

3509 [file_selector_platform_interface] File selector nnbd (cla: yes, nnbd, p: file_selector, platform-web)