clang-format: [JS] Indent expressions in ${} relative to their surrounding

This only affects expressions inside ${} scopes of template strings.
Here, we want to indent relative to the surrounding template string and
not the surrounding expression. Otherwise, this can create quite a mess.

Before:
  var f = `
    aaaaaaaaaaaaaaaaaa: ${someFunction(
      aaaaa +  //
      bbbb)}`;

After:
  var f = `
    aaaaaaaaaaaaaaaaaa: ${someFunction(
                              aaaaa +  //
                              bbbb)}`;

llvm-svn: 293636