Allow users of components using withTheme to pass theme styles (#191)
Allow users of components using withTheme to pass theme styles (#191)

We initially didn't expose the `snacksTheme` prop to users
because we didn't need to, and smaller surface areas are usually
a good thing.

Recently we had a few use cases where we wanted to lock in a
particular theme for a subset of snacks components, so this commit
allows users to pass in a custom `snacksTheme` prop to any components
that use `withTheme`.
instacart/Snacks,instacart/Snacks,instacart/Snacks