Use isCharInSet from llvm/Support/UnicodeCharRanges.h, added a test for double-width characters in FixIt-hints.

Summary: This is a follow-up to r187837.

Reviewers: gribozavr, jordan_rose

Reviewed By: jordan_rose

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1306

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@188056 91177308-0d34-0410-b5e6-96231b3b80d8