IDE functionality needs some internal type checking logics, e.g. checking
whether an extension is applicable to a concrete type. We used to directly
expose an header from sema called IDETypeChecking.h so that IDE functionalities
could invoke these APIs. The goal of the commit and following commits is to
expose evaluator requests instead of directly exposing function entry points from
sema so that we could later move IDETypeChecking.h to libIDE and implement these functions
by internally evaluating these requests.
Resolving cursor info is a necessary step both when checking the availability
of a refactoring kind and performing the refactoring action. These
two steps are two high-level sourcekitd requests issued from IDE.
By caching the result of the resolved cursor info in the evaluator of
the ASTContext, we can reuse the cursor info result across these separate
IDE requests.
