[dev.typeparams] Fix problem with 14.go

Removed a case in transformCall() where we were setting a type on n,
which isn't needed, since noder2 already set the type of n. More
importantly, we are losing information, since the type of the results
may be a shape type, but the actual type of call is the known type
from types2, which may be a concrete type (in this case Zero[MyInt]).
That concrete type will then be used correctly if the concrete result is
converted to an interface.

If we are inlining the call to Zero[MyInt], we need to add an implicit
CONVNOP operation, since we are going to use the result variable
directly, which has a shape type. So, add an implicit CONVNOP to
remember that the known type is the concrete type.

Also cleaned up 14.go a bit, so it is more understandable. Renamed type
T to AnyInt, since T is used elsewhere as a type parameter. Reformatted
Zero function and added a comment.

Change-Id: Id917a2e054e0bbae9bd302232853fa8741d49b64
Reviewed-on: https://go-review.googlesource.com/c/go/+/336430


Trust: Dan Scales <danscales@google.com>
Reviewed-by: Keith Randall <khr@golang.org>