Lang: re-provided type from one module incompatible with origin module

[alex-snezhko]

// c.gr
module C
provide record T {
  x: Number
}

// b.gr
module B
include "./c"
from C use { type T }
let a = { x: 1 }
provide { type T, a }

// a.gr
module A
include "./b"
from B use { type T, a }
print(a == { x: 1 })

The above code fails to compile with the error

Error: This expression has type B.T but an expression was expected of type
         C.T
C::T is abstract because no corresponding cmi file was found in path.

[peblair]

I have not come up with a fix yet, but a preliminary look says that the root cause here is the type_manifest field not getting set on B.T at import time (see Env.use_partial_signature). This field is used in the unification engine to handle type T = T0-type declarations in OCaml, so hopefully getting it wired up fixes the issue.