Implement GenericRequirement support for member type disambiguation

[art-divin]

Resolves #1087

Context

This PR adds implements to Type & co, so that it is now possible to preserve information about protocol requirements during deserialization of variables and method-related types.

In particular, for cases like:

struct GenericStruct<T>: Equatable where T: Equatable {
  func method(_ arg: T) {}
}

method's argument type's actualTypeName is resolved to (Equatable) instead of simply T.
Before this PR, it was resolved to nil.

Let's also consider the following use case with protocol composition:

struct GenericStruct<T>: Equatable where T: Equatable, T: Codable {
  let value: T
}

here, variable's type is resolved as a ProtocolComposition type with Codable and Equatable Protocol instances bound together, that is, actualTypeName becomes (Codable & Equatable) respectively.