If a field and method have the same name, mark the respective struct field
so that we don't report follow-on errors when the field/method is accessed.

Per suggestion of @mdempsky.

Fixes #28268.

Change-Id: Ia1ca4cdfe9bacd3739d1fd7ca5e014ca094245ee
Reviewed-on: https://go-review.googlesource.com/c/144259Reviewed-by: Matthew Dempsky <mdempsky@google.com>