[dev.typeparams] go/*: add TODOs from CLs importing dev.go2go changes

With the plurality of CLs importing dev.go2go changes it's getting hard
to track all of the code review comments that were deferred for later
consideration. Add some TODOs to capture these comments in the source,
so that they may be more easily located.

Change-Id: I5caf085fec11ca8992b7affe6feb0a7aa202f21f
Reviewed-on: https://go-review.googlesource.com/c/go/+/276254


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>