[completion] complete ObjC interface names in an expression

Objective-C interfaces can be used in a class property expression.

rdar://26982192

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@318129 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 36748ae0097a3558204dd653c549bba2b7ae7431)
3 files changed