Integrate MultiVerb into the `servant` packages

[theophile-scrive]

This commit is Part 1 of the integration, where only the packages of this monorepo are touched. Verb is redefined as an alias for MultiVerb1 in order to make the transition transparent to users of Verb.

• MultiVerb is thus used instead of Verb for type family instances

Compared to the original implementation:

• IsWaiBody will not be able to live in its current form, as it mixes concepts from the Server and Client packages.

  • This impacts SomeResponse, which itself impacts the HasClient and HasServer instances.
  • ResponseF can be replicated internally, even without the httpVersion field.

• SomeResponse can be kept on the server, but the client can move to use ResponseF.

• OpenAPI (and Swagger) support libraries will have such a definition

  instance (ToSchema a, Accept ct, KnownNat status, OpenApiMethod method)
  => HasOpenApi (Stream method status fr ct a) where
  toOpenApi _ = toOpenApi (Proxy :: Proxy (MultiVerb method status '[ct] (Headers '[] a)))

Where method is constrained to be an OpenApiMethod. However the original implementation locks the type to be a StdMethod

In contrast, Verb's original definition kept the method polymorphic:

data Verb (method :: k1) (statusCode :: Nat) (contentTypes :: [*]) (a :: *)

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This is a collaborative work between Scrive AB and Wire Swiss GmbH.