Adjust the implements clause of IntX (#866)

Co-authored-by: Devon Carew <devoncarew@google.com>

Author: eernstg

pkgs/fixnum/CHANGELOG.md

@@ -1,3 +1,9 @@
+## 1.2.0-wip
+
+* Change `IntX` such that it implements `Comparable<IntX>`. This makes it
+  possible for `IntX` (and in turn `Int64` and `Int32`) be used with methods
+  like `sortedBy` in the platform libraries.
+
 ## 1.1.1
 
 * Require Dart `^3.1.0`

pkgs/fixnum/lib/src/intx.dart

@@ -6,7 +6,7 @@ import 'int32.dart';
 import 'int64.dart';
 
 /// A fixed-precision integer.
-abstract class IntX implements Comparable<Object> {
+abstract class IntX implements Comparable<IntX> {
   /// Addition operator.
   IntX operator +(Object other);
 

pkgs/fixnum/pubspec.yaml

@@ -1,5 +1,5 @@
 name: fixnum
-version: 1.1.1
+version: 1.2.0-wip
 description: >-
   Library for 32- and 64-bit signed fixed-width integers with consistent
   behavior between native and JS runtimes.