Import by hash: Imported modules should be added to autocomplete

Symbols in modules that are imported by hash currently don't appear in autocomplete, doc-on-hover, etc. This is too bad. One could imagine having the client ask for the code, and process it in the same way it does the current module.

One complication: if the module is imported by deploy hash (DXXXX instead of PXXXX), then the client will not be able to request the code. This is intentional. For instance, @nomeata requested deploy hashes initially for CIS 194, and used them to show students their goal in an assignment without giving them the source code. If they could import the deploy hash and see the exported symbols and types and docs, this would be leaking info about Joachim's assignment solutions that he (and others using the same content or feature) likely didn't intend to share. In the current design, there is no official distinction between library and executable projects, so if we carved out some kind of hole, it would apply to all projects.