cmd/go/internal/load: load imports for all package data errors
go/build.Import can return errors for many different reasons like
inconsistent package clauses or errors parsing build constraints.
It will still return a *build.Package with imports from files it was
able to process. Package.load should load these imports, even after an
unknown error.
There is already a special case for scanner.ErrorList (parse
error). This CL expands that behavior for all errors.
Fixes #38568
Change-Id: I871827299c556f1a9a5b12e7755b221e9d8c6e0e
Reviewed-on: https://go-review.googlesource.com/c/go/+/229243 Reviewed-by: Bryan C. Mills <bcmills@google.com>