[index/AST] Add references for ObjC getter=/setter= property attributes and...

[index/AST] Add references for ObjC getter=/setter= property attributes and related property getter/setter role fixes

This enhances the AST to keep track of locations of the names in those ObjC property attributes, and reports them for indexing.

Patch by Nathan Hawes!
https://reviews.llvm.org/D30907

llvm-svn: 297972