Fix typechecker crash on non elixir struct module in defimpl

[lukaszsamson]

Ensure the module exports info/1
Mimic check from struct_info/6

This PR fixes typechecker crash on the following code:

    defprotocol OxP do
      def f(x)
    end

    defimpl OxP, for: :gen_server do
      def f(x), do: x
    end

    == Compilation error in file repro.exs ==
    ** (UndefinedFunctionError) function :gen_server.__info__/1 is undefined or private
        (stdlib 7.3) :gen_server.__info__(:struct)
        (elixir 1.21.0-dev) lib/module/types/of.ex:294: Module.Types.Of.impl/2
        (elixir 1.21.0-dev) lib/module/types.ex:154: Module.Types.default_domain/4
        (elixir 1.21.0-dev) lib/module/types.ex:297: Module.Types.local_handler/5

The code is invalid but it should not crash the typechecker. We can think if defimpl could error on compilation

AssistedBy: test created with Claude Opus 5

[josevalim]

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