go/types: update the recorded function type after inference
This change preserves the observable invariant that for an *ast.CallExpr
'call', Info.Types[call.Fun] is the signature being called.
Updates #47916
Change-Id: I3e97c712a7ee33a4f29e8cf4c18dc7c946b66cc9
Reviewed-on: https://go-review.googlesource.com/c/go/+/353831
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Robert Griesemer <gri@golang.org>