Support documentation comments in destructured `export const`

[marrus-sh]

The following does not appear to be supported currently :—

export const {
  /** Some thing. */
  someThing,
  /** Some other thing. */
  someOtherThing,
} = (() => {
  // An IIFE is needed here if you want to dynamically determine the value of these `const`s.
  // This is also useful for scoping purposes.
  return { someThing: "etaoin", someOtherThing: "shrdlu" };
})();

Possibly related to #92 or #247 but this is specifically for destructured export const.