[dev.typeparams] cmd/compile: fix unified IR support for //go:nointerface

This CL changes fixedbugs/issue30862.go into a "runindir" test so that
it can use '-goexperiment fieldtrack' and test that //go:nointerface
works with cmd/compile. In particular, this revealed that -G=3 and
unified IR did not handle it correctly.

This CL also fixes unified IR's support for //go:nointerface and adds
a test that checks that //go:nointerface, promoted methods, and
generics all interact as expected.

Updates #47045.

Change-Id: Ib8acff8ae18bf124520d00c98e8915699cba2abd
Reviewed-on: https://go-review.googlesource.com/c/go/+/332611


Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>