Migrate pkg/expect to the new constructor syntax.

Change-Id: I872868b7f9dea21889aeac00a92eef0b03849354
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/506603
Auto-Submit: Bob Nystrom <rnystrom@google.com>
Commit-Queue: Bob Nystrom <rnystrom@google.com>
Reviewed-by: Paul Berry <paulberry@google.com>

pkg/expect/analysis_options.yaml

@@ -7,3 +7,5 @@ analyzer:
 linter:
   rules:
     - lines_longer_than_80_chars
+    - unnecessary_const_in_enum_constructor
+    - unnecessary_type_name_in_constructor

pkg/expect/lib/expect.dart

@@ -913,7 +913,7 @@ class ExpectException {
   final String message;
   final String name;
 
-  ExpectException(this.message) : name = _getTestName();
+  new(this.message) : name = _getTestName();
 
   @override
   String toString() {

pkg/expect/lib/legacy/minitest.dart

@@ -208,5 +208,5 @@ class _Group {
 class _Expectation {
   final _ExpectationFunction function;
 
-  _Expectation(this.function);
+  new(this.function);
 }

pkg/expect/pubspec.yaml

@@ -10,7 +10,7 @@ description: >-
 publish_to: none
 
 environment:
-  sdk: '^3.12.0-0'
+  sdk: '^3.13.0-0'
 
 resolution: workspace
 

pkg/expect/test/identical_distinct_test.dart

@@ -87,7 +87,7 @@ void main() {
 
 class C {
   final Object x;
-  const C(this.x);
+  const new(this.x);
   @override
   int get hashCode => x.hashCode;
   @override