[libclang] Introduce clang_Cursor_getObjCSelectorIndex() function.

After getting a cursor with clang_getCursor for a particular source location,
allows querying the cursor in order to find out if the location points to a
selector identifier in an objc method or message expression, and which selector index it is.

rdar://11158946

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@153781 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed