RFC: don't preserve line breaks in object literals if all the properties are shorthand

Let's format

const name = {
  firstName,
  lastName,
};

into

const name = { firstName, lastName };

Thoughts? Counterexamples?

Update, based on the discussion below:

Line breaks should not be preserved if

• all the properties are shorthand or
• the first property is a spread whose operand is an identifier and the rest of the properties are shorthand.

If the object literal contains empty lines or comments, line breaks should be preserved (the current behavior is kept).

Start by reproducing the object-literal examples in the issue with the formatter and reviewing the current behavior for shorthand properties, identifier spreads, comments, and empty lines. Done means the stated line-break rules are implemented without changing preservation around comments or empty lines, with formatting behavior verified against the examples.