[index] ObjC: Improve handling of typedefs as base names in ObjC interface declarations

- Report the typedef reference occurrence
- Mark super or protocol references as 'implicit' when they come from a typedef.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@296974 91177308-0d34-0410-b5e6-96231b3b80d8