Updates dartc to recognize 'default' keyword on interface and updated factory method syntax

tests/stub-generator/src/MintMakerFullyIsolatedTest.dart

Index: tests/stub-generator/src/MintMakerFullyIsolatedTest.dart
diff --git a/tests/stub-generator/src/MintMakerFullyIsolatedTest.dart b/tests/stub-generator/src/MintMakerFullyIsolatedTest.dart
index 0a0e61243420224df9d1135a8c1831071d6fabc8..63ed54057bfe8372e458b2ea3c057ba8f1263007 100644
--- a/tests/stub-generator/src/MintMakerFullyIsolatedTest.dart
+++ b/tests/stub-generator/src/MintMakerFullyIsolatedTest.dart
@@ -15,7 +15,7 @@ interface Purse {
   Promise<int> deposit(int amount, Purse$Proxy source);
 }
 
-interface PowerfulPurse extends Purse factory PurseImpl {
+interface PowerfulPurse extends Purse default PurseImpl {
   PowerfulPurse();
 
   void init(Mint$Proxy mint, int balance);
@@ -25,7 +25,7 @@ interface PowerfulPurse extends Purse factory PurseImpl {
   Purse weak();
 }
 
-interface Mint factory MintImpl {
+interface Mint default MintImpl {
   Mint();
 
   Purse$Proxy createPurse(int balance);