Rethink usage tracking of union members for Hive App UI

Union type field usage is shown as 1.8k times.
Clicking on the same field in explorer, shows zero usage

We don’t track members of a union directly, we track types and fields of these members.
Let’s say you have `Query.media` that resolves Media union, that has `TV` and `Radio` members.
When querying `Query.media`, for Hive does not matter if it’s a union or an interface as you use fragments there anyway.
These fragments (spreads or inlines) tell Hive what you are querying there.

When querying `.__typename`, we do mark the union as used though. This way we “lock” the union type, so whenever you modify its members, we treat it as a breaking change.
It’s not ideal, but it’s only affecting the UI part of Hive.

We will double-think if tracking the names of union members makes sense and won’t cause damage.