Array::push and others explicitly apply default formatting, rather than implicitly.

[epage]

Found via rust-lang/cargo#15084 where a &str was pushed into an Array and then sort_by_keyed. This made it so the formatting applied by push was not relevant. If we delay until we render, then we'll know how to handle this.

The default formatting was added in #88. I think after that we added the tracking of "this is in a default state" and wouldn't need this anymore.