[analyzer] JsonSupport: Escape escapes

Summary: -

Reviewers: NoQ

Reviewed By: NoQ

Subscribers: xazax.hun, baloghadamsoftware, szepet, a.sidorin,
             mikhail.ramalho, Szelethus, donat.nagy, dkrupp, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D63462

llvm-svn: 364270