Re-export cache types from @apollo/client/core, again. (#6725)
Re-export cache types from @apollo/client/core, again. (#6725)

These types were lost in #6656 when I switched from

  export * from '../cache'

to using named exports. There are some @apollo/client/cache exports that I
wanted to omit from @apollo/client/core (like cacheSlot), but I definitely
did not intend to omit these types.

Fixes #6723.
apollographql/apollo-client,apollographql/apollo-client,apollostack/apollo-client,apollostack/apollo-client,apollostack/apollo-client