[dev.typeparams] cmd/compile: make sure types added to the dictionary are instantiated correctly

Make sure the instantiating types are the type parameters of the containing
function (or types derived from those).

The one exception is the argument of a OFUNCINST, whose type
parameters are those of the declaration site of the function or method
being instantiated. We skip those types.

Change-Id: I4b3ff22eb8a81a76476930cf8ed2a7dd6489d8b8
Reviewed-on: https://go-review.googlesource.com/c/go/+/336352


Trust: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>