SnackbarProvider has incorrect typing for iconVariant

[amakhrov]

The current definition is

iconVariant?: React.ComponentType<SvgIconProps>;

which doesn't match the actual prop type defined in the component (.js file):

iconVariant: PropTypes.shape({
        /**
         * Icon displayed when variant of a snackbar is set to `success`.
         */
        success: PropTypes.any.isRequired,
        /**
         * Icon displayed when variant of a snackbar is set to `warning`.
         */
        warning: PropTypes.any.isRequired,
        /**
         * Icon displayed when variant of a snackbar is set to `error`.
         */
        error: PropTypes.any.isRequired,
        /**
         * Icon displayed when variant of a snackbar is set to `info`.
         */
        info: PropTypes.any.isRequired,
    }),