1816 [firebase_messaging] add integration tests (cla: yes)

1817 [image_picker]use class instead of struct for GIFInfo on iOS (cla: yes)

1818 [firebase_messaging] Change signature of subscribe/unsubscribe (cla: yes)

1819 [in_app_purchase] iOS: Support unsupported UserInfo value types on NSError. (cla: yes, submit queue)

1822 [Connectivity] Fixes issue “connectivity using deprecated api” (cla: yes, submit queue)

1823 [image_picker] Update README example (cla: yes)

1826 [firebase_auth] Register for iOS notifications to support phone auth (cla: yes)

1827 [in_app_purchase] fix version (cla: yes)