The logic to resolve the enclosing type for an identifier is somewhat
tricky. Add a unit test to exercise a few edge cases.
This would probably be easier to read and write using a hybrid approach
that extracts markers from the source.
This test uncovered a bug, that on the SelectorExpr branch we were
accidentally returning a nil *Named types.Type, rather than a nil
types.Type.
Change-Id: I43e096f51999b2a6e109c09d3805ad70a4780398
Reviewed-on: https://go-review.googlesource.com/c/tools/+/244841
Reviewed-by: Heschi Kreinick <heschi@google.com>
