Fix fragment sorting (#347)

Author: Shane32

src/GraphQLParser.Tests/Visitors/SDLSorterTests.SortsSchemaDefinition.approved.ExecutableSortTests.graphql

@@ -53,11 +53,11 @@ subscription s3 @dir1 @dir2 @dir3 {
   dummy
 }
 
-fragment frag2 on Type1 {
+fragment frag1 on Type2 {
   dummy
 }
 
-fragment frag1 on Type2 {
+fragment frag2 on Type1 {
   dummy
 }
 

src/GraphQLParser/Visitors/SDLSorterOptions.cs

@@ -63,6 +63,7 @@ public virtual int Compare(ASTNode x, ASTNode y)
             GraphQLFragmentSpread x => x.FragmentName.Name.Value,
             GraphQLRootOperationTypeDefinition x => x.Operation switch { OperationType.Query => "a", OperationType.Mutation => "b", _ => "c" },
             GraphQLVariableDefinition x => x.Variable.Name.Value,
+            GraphQLFragmentDefinition x => x.FragmentName.Name.Value,
             _ => "", // do not sort values, comments, etc
         };
     }