clang-format: [JS] Support for (.. of ..) loops.

Before:
  for (var i of[2, 3]) {}

After:
  for (var i of [2, 3]) {}

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@260518 91177308-0d34-0410-b5e6-96231b3b80d8