servo: Merge #20583 - selectors: Don't serialize :nth-child(-n) as -1n (from emilio:affine-stuff); r=upsuper

Source-Repo: https://github.com/servo/servo
Source-Revision: ecfcf35c26e789bacd2c46786bf0d75f0b20944f

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : e8e1b6c86a62fda25f755b021eab13da3173aa22

servo/components/selectors/parser.rs

@@ -1021,6 +1021,7 @@ impl<Impl: SelectorImpl> ToCss for Component<Impl> {
                 (0, 0) => dest.write_char('0'),
 
                 (1, 0) => dest.write_char('n'),
+                (-1, 0) => dest.write_str("-n"),
                 (_, 0) => write!(dest, "{}n", a),
 
                 (0, _) => write!(dest, "{}", b),