Implement Int64 as a wrapper for int when targeting native and Wasm

pkgs/fixnum/CHANGELOG.md

@@ -4,6 +4,7 @@
   possible for `IntX` (and in turn `Int64` and `Int32`) be used with methods
   like `sortedBy` in the platform libraries.
 - Run `dart format` with the new style.
+- Improve `Int64` representation when compiling to native or Wasm.
 
 ## 1.1.1
 

pkgs/fixnum/lib/fixnum.dart

@@ -4,8 +4,8 @@
 
 /// Signed 32- and 64-bit integer support.
 ///
-/// The integer implementations in this library are designed to work
-/// identically whether executed on the Dart VM or compiled to JavaScript.
+/// The integer implementations in this library are designed to work identically
+/// whether executed on the Dart VM or compiled to JavaScript or Wasm.
 library;
 
 export 'src/int32.dart';

pkgs/fixnum/lib/src/int32.dart

@@ -321,8 +321,6 @@ class Int32 implements IntX {
     return Int32(value);
   }
 
-  /// Returns [:true:] if this [Int32] has the same numeric value as the
-  /// given object.  The argument may be an [int] or an [IntX].
   @override
   bool operator ==(Object other) {
     if (other is Int32) {