title: gazelle+protobuf problem: does not have mandatory providers: 'GoLibrary'
body: <p>From gazelle-generated BUILD files, I get the following error when I run <code>bazel build //foo/bar/protos/...:</code></p>
  <p><code>ERROR:  .../foo/bar/protos/BUILD.bazel:15:17: in deps attribute of go_proto_library rule //foo/bar/protos:protos_go_proto: '//baz/quux/api:api_proto' does not have mandatory providers: 'GoLibrary'</code></p>
  <p>Both BUILD files have:</p>
  <pre><code>load(&quot;@rules_proto//proto:defs.bzl&quot;, &quot;proto_library&quot;)
  load(&quot;@io_bazel_rules_go//go:def.bzl&quot;, &quot;go_library&quot;)
  load(&quot;@io_bazel_rules_go//proto:def.bzl&quot;, &quot;go_proto_library&quot;)
  </code></pre>
  <p>I have seen <code>https://github.com/bazelbuild/rules_go/blob/master/go/providers.rst</code>, but it was more confusing.</p>
  <p><em>I also asked this on the Gophers Slack, but there is very little traffic there.</em></p>