Formatter puts external bindings on the same line as their doc comments

[johnridesabike]

This code:

/**
  Does something.
 */
@val external foo: unit => unit = "foo"

/**
  Does something else
 */
let bar = () => ()

Formats to this:

/**
  Does something.
 */ @val external foo: unit => unit = "foo"

/**
  Does something else
 */
let bar = () => ()

This seems to be a regression in v10

[cristianoc]

Thanks for the report.

Seems to be about doc comments and attributes #642