Remove `addTypename` exchange to be agnostic to GQL client

[IzumiSy]

Currently, fabrix internally depends on urql, but we have a plan to make it pluggable by #123

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Background

__typename is needed for fabrix to look up the field type, so fabrix has a custom exchange (addTypename) for urql to add __typename automatically.

https://github.com/fabrix-framework/fabrix/blob/main/packages/fabrix/src/exchanges/addTypename.ts

However, to be agnostic to GQL client, it should be handled independently in the layer of GraphQL visitor instead of exchanges.