Extend the type checking context to allow de-duplicating *Signature
instances, in addition to *Named instances.
Naively we would deduplicate instances of different-but-identical origin
*Signature types. That may be OK, but it seems a bit strange to get the
same signature when instantiating two different functions. For now,
differentiate *Signature types by prepending a unique identifier for the
origin pointer, thus guaranteeing that instances de-duplicated if they
come from the exact same (pointer identical) origin type.
Updates #47103
Change-Id: I93cc3cacad195267fe0a5801f9c5a3b1e61eb907
Reviewed-on: https://go-review.googlesource.com/c/go/+/362801
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>