[Chips] add NS_ASSUME_NONNULL_BEGIN annotation.
[Chips] add NS_ASSUME_NONNULL_BEGIN annotation.

PiperOrigin-RevId: 485345704

material-components/material-components-ios,material-components/material-components-ios,material-components/material-components-ios,material-components/material-components-ios,material-components/material-components-ios