Definition::visibility was implemented in a rather roundabout way -- by
asking the parent module about the effective visibility.
This is problematic for a couple of reasons:
* first, it doesn't work for local items
* second, asking module about visibility of a child is a linear
operation (that's a problem in itself, tracked in #9378)
Instead, lets ask the declared visibility directly, we have all the code
for it, and need only to actually us it.
7be2d2f008