Teach code completion to adjust its completion priorities based on the

type that we expect to see at a given point in the grammar, e.g., when
initializing a variable, returning a result, or calling a function. We
don't prune the candidate set at all, just adjust priorities to favor
things that should type-check, using an ultra-simplified type system.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@105128 91177308-0d34-0410-b5e6-96231b3b80d8