Use field init shorthand where possible

Field init shorthand allows writing initializers like `tcx: tcx` as
`tcx`. The compiler already uses it extensively. Fix the last few places
where it isn't yet used.

compiler/rustc_parse/src/parser/pat.rs

@@ -1648,7 +1648,7 @@ impl<'a> Parser<'a> {
                 ident: prev_field,
             })
         } else {
-            self.dcx().create_err(AtInStructPattern { span: span })
+            self.dcx().create_err(AtInStructPattern { span })
         }
     }