[clangd] Fixed toHalfOpenFileRange

Summary:
- Fixed toHalfOpenFileRange to work for macros as well as template
instantiations
- Added unit tests

Breaking test case for older version of toHalfOpenFileRange:
\# define FOO(X) X++
int a = 1;
int b = FOO(a);
toHalfOpenFileRange for the sourceRange of VarDecl for b returned the
wrong Range.

Reviewers: sammccall, kadircet

Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D64562

llvm-svn: 365894