clang-format: [JS] Support quoted object literal keys.

Before:
  var x = {
    a: a,
    b: b, 'c': c,
  };

After:
  var x = {
    a: a,
    b: b,
    'c': c,
  };

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@262291 91177308-0d34-0410-b5e6-96231b3b80d8