Field identifiers now include specific spans (Closes #8263).
#8263 part 2: Adding struct name.
auto merge of #10142 : pythonesque/rust/issue-8263, r=catamorphism

This is, I think, the minimal change required.  I would have included a test but as far as I can tell there is currently no way to precisely test that the span for an error underlines the correct word.  I did verify it manually.