Structure visualization doesn't exhaust parents

From mps-langvis created by [eugenschindler](https://github.com/eugenschindler): DSLFoundry/mps-langvis#4

The structure visualization should, similar to the context visualization, exhaustively visualize the parent's structure.

Start by locating the structure-visualization entry point in the MPS-extensions repository and compare it with the context visualization mentioned in the issue. The work is done when the structure view exhaustively visualizes the parent structure in the same relevant cases as the context view; no file or test is named in the issue.

Written by the indexing model from the issue text.