Add contextual information to lookup queries and fix a pre-render bug
Add contextual information to lookup queries and fix a pre-render bug

This sets the stage to get context-dependent information in lookups.

The pre-render bug was that our implementation of `pre-render would shorten the
candidate, which would confuse company when the longest common prefix was the
whole candidate.

FStarLang/fstar-mode.el,FStarLang/fstar-mode.el,FStarLang/fstar-mode.el