clang-format: [JS] Add a special case for indenting function literals.

Before:
  var func =
      function() {
        doSomething();
      };

After:
  var func =
      function() {
    doSomething();
  };

This is a very narrow special case which fixes most of the discrepency
with what our users do. In the long run, we should try to come up with
a more generic fix for indenting these.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@240014 91177308-0d34-0410-b5e6-96231b3b80d8