Implement semantic selections.

Summary:
For a given cursor position, it returns ranges that are interesting to the user.
Currently the semantic ranges correspond to the nodes of the syntax trees.

Subscribers: mgorny, jkorous, arphaman, kadircet, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D67358

llvm-svn: 371976
GitOrigin-RevId: 73c09eb7344e103f126811a7e6c670ddfa5fb771
5 files changed