Reorder fullfillment errors to keep more interesting ones first

In `report_fullfillment_errors` push back `T: Sized`, `T: WellFormed`
and coercion errors to the end of the list. The pre-existing
deduplication logic eliminates redundant errors better that way, keeping
the resulting output with fewer errors than before, while also having
more detail.

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -368,7 +368,7 @@ fn check_opaque_type_well_formed<'tcx>(
     if errors.is_empty() {
         Ok(definition_ty)
     } else {
-        Err(infcx.err_ctxt().report_fulfillment_errors(&errors))
+        Err(infcx.err_ctxt().report_fulfillment_errors(errors))
     }
 }