formatter won't keep multiline for exceptions

how to test:

1. type type t = {name: string, msg: string} and run formatter
2. notice still single line
3. type

type t = {
  name: string,
  msg: string,
}

and run formattter
4. notice still four lines
5. type exception Foo({name: string,msg: string}) and run formatter
6. notice still single line
7. type

exception Foo({
  name: string,
  msg: string,
})

and run formatter
8. BUG: formatter forces it to single line

Start by reproducing the numbered examples with the formatter, comparing the single-line and multiline forms for records and exceptions. Trace the formatter code reached by these inputs; done means intentionally multiline records and exception payloads remain multiline instead of being forced to one line.