Verify StringBuilder and MemoryStream writing is synchronous (#276)

Author: Shane32

src/GraphQLParser.Tests/Visitors/SDLPrinterTests.cs

@@ -1,3 +1,4 @@
+using System.Text;
 using GraphQLParser.Visitors;
 
 namespace GraphQLParser.Tests.Visitors;
@@ -750,6 +751,26 @@ public async Task Directive_Without_Parent_Should_Be_Printed()
         writer.ToString().ShouldBe("@upper");
     }
 
+    [Fact]
+    public void StringBuilder_Runs_Synchronously()
+    {
+        var document = "KitchenSink".ReadGraphQLFile().Parse();
+        var sb = new StringBuilder();
+        using var writer = new StringWriter(sb);
+        var printer = new SDLPrinter();
+        printer.PrintAsync(document, writer).IsCompletedSuccessfully.ShouldBeTrue();
+    }
+
+    [Fact]
+    public void UTF8_MemoryStream_Runs_Synchronously()
+    {
+        var document = "KitchenSink".ReadGraphQLFile().Parse();
+        using var ms = new MemoryStream();
+        using var writer = new StreamWriter(ms);
+        var printer = new SDLPrinter();
+        printer.PrintAsync(document, writer).IsCompletedSuccessfully.ShouldBeTrue();
+    }
+
     [Theory]
     [InlineData("query a { name }")]
     [InlineData("directive @skip(if: Boolean!) on FIELD | FRAGMENT_SPREAD | INLINE_FRAGMENT")]