swift234

Code completion: report "semantic context" for every code completion result

Semantic context describes the origin of the declaration and serves the same
purpose as opaque numeric "priority" in Clang -- to determine the most likely
completion.

This is the initial implementation.  There are a few opportunities to bump the
priority of a certain decl by giving it SemanticContextKind::ExprSpecific
context that are not implemented yet.


Swift SVN r9052