Fix aliasAs generating wrong type for the alias variable

[dillonkearns]

When using Elm.Arg.aliasAs on a record pattern, the alias variable was incorrectly using a fresh type variable instead of inheriting the underlying pattern's type.

For example, here's what this snippet generates:

Arg.record ... |> Arg.field "name" |> Arg.aliasAs "person"

Before:

{ name : name, age : age } -> ( name, person )

(person is wrong - should be the record type)

After:

{ name : name, age : age } -> ( name, { name : name, age : age } )

Root cause: aliasAs was calling val which creates a fresh GenericType for the alias name. The fix uses the inner pattern's annotation (the actual record/tuple/etc type) for the alias value.