Replace all ~"" with "".to_owned()
auto merge of #13548 : richo/rust/remove_owned_string_literal, r=brson

Had a quick stab at this with a sed macro.

Fixed a lot of strings, but there's a bunch of tidy errors because of the increased line lengths now, definitely some broken tests, and isn't complete.

Pushing purely so that there's state on this. /cc #13543