3628 [google_sign_in_web] Migrate to null-safety (cla: yes, nnbd, p: google_sign_in, platform-web, waiting for tree to go green)

3630 [file_selector] Return a non-null value from getSavePath on web (cla: yes, p: file_selector, platform-web, waiting for tree to go green)

3635 [image_picker_for_web] Bump version for NNBD stable (cla: yes, p: image_picker, platform-web, waiting for tree to go green)

3652 [connectivity_for_web] Migration to null-safety. (cla: yes, p: connectivity, platform-web, waiting for tree to go green)