go/types, types2: clarify docs for resolveUnderlying
The resolveUnderlying method only detects cycles among type names, where
no type literal or predeclared type can be found (which would yield an
underlying type).
Change-Id: I203f3856eaf63a8a9d317c22521755390f9c1023
Reviewed-on: https://go-review.googlesource.com/c/go/+/714402 Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Mark Freeman <markfreeman@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>