[dev.typeparams] test: add expected failure mechanism

This CL changes the existing excluded-test mechanism into a
known-failure mechanism instead. That is, it runs the test regardless,
but only reports if it failed (or succeeded) unexpectedly.

It also splits the known failures list into fine-grain failure lists
for types2, types2 w/ 32-bit target, -G=3, and unified.

Updates #46704.

Change-Id: I1213cbccf1bab6a92d9bfcf0d971a2554249bbff
Reviewed-on: https://go-review.googlesource.com/c/go/+/332551


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