[AutoDiff] Remap apply callee type in derivative context.

[dan-zheng]

Previously, LinearMapInfo::addLinearMapToStruct did not remap apply callee
type in derivative context.

Now, remapping is done. Remapping is significant when the derivative has a
more constrained generic signature.

Resolves TF-817.

---

Reproducer:

extension Array {
  @differentiable(wrt: self where Element : Differentiable)
  public func foo(index: Int) -> Element {
    return self[0]
  }
}

# 'self` wrt parameter type.

# Before: 
(bound_generic_struct_type decl=Swift.(file).Array
  (primary_archetype_type address=0x7fba3e0e1990 name=Element
))

# After:
(bound_generic_struct_type decl=Swift.(file).Array
  (primary_archetype_type address=0x7fba3d95e008 conforms_to=Swift.(file).Differentiable name=τ_0_0

    (nested_type=TangentVector <<unresolved>>)))

[dan-zheng]

Note: the actual fix is relatively small (9fffe89).
I also included NFC gardening (0501f5f) to save time.

[dan-zheng]

@swift-ci Please test tensorflow

[rxwei]

@swift-ci Please test tensorflow