Run rustfmt and keep it running on CI (#2023)

Thought we did this awhile back, but looks like we forgot to do so!

crates/backend/src/codegen.rs

@@ -42,7 +42,8 @@ impl TryToTokens for ast::Program {
             DescribeImport {
                 kind: &i.kind,
                 unstable_api: i.unstable_api,
-            }.to_tokens(tokens);
+            }
+            .to_tokens(tokens);
 
             // If there is a js namespace, check that name isn't a type. If it is,
             // this import might be a method on that type.

crates/backend/src/util.rs

@@ -157,7 +157,6 @@ impl<T: Hash> fmt::Display for ShortHash<T> {
     }
 }
 
-
 /// Create syn attribute for `#[cfg(web_sys_unstable_apis)]` and a doc comment.
 pub fn unstable_api_attrs() -> proc_macro2::TokenStream {
     quote::quote!(