go/types, types2: make Checker.renameTParams work on any type

go/types, types2: make Checker.renameTParams work on any type

This permits the rewrite of type parameters in arbitrary types,
not just tuples.

Preparation for fixing #59956.
For #59338.

Change-Id: I9ccaac1f163051cb837cae2208763cafb1d239cb
Reviewed-on: https://go-review.googlesource.com/c/go/+/492515
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>