Export style type

[java-james]

By exporting the style type it will be easier for consumers to build the correct prop when using the library with typescript.

eg add

export type GradientBorderViewStyle = StyleProp<
            GradientBorderViewProps & 
            {paddingLeft?: number, paddingRight?: number, paddingTop?: number, paddingBottom?: number, padding?: number}
        >

Can use internally as needed eg:

export default function GradientBorderView({
    gradientProps,
    ...props
}: Omit<ViewProps, 'style'> &
    {
        style?: GradientBorderViewStyle
    } &
    RequiredGradientBorderProps
) {