cmd/compile/internal/types2: revert to three-phase alias resolution
This change reenables the legacy three-phase resolution
(non-alias typenames, aliases, the rest) even when
GODEBUG=gotypesalias=1. Unfortunately the existing test case
for #50259 causes the simpler logic to fail.
Updates #50259
Updates #65294
Change-Id: Ibfaf8146e46760718673a916a9b220a9d678409a
Reviewed-on: https://go-review.googlesource.com/c/go/+/577616 Reviewed-by: Matthew Dempsky <mdempsky@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>