Tests/LibWeb: Verify setting {readable,writable}Type throws RangeError

This test proves that setting transformer.{readable,writable}Type to a
value throws a RangeError.

Tests/LibWeb/Text/expected/Streams/TransformStream-readableType-writableType-has-value.txt

@@ -0,0 +1,2 @@
+'readableType' => Exception raised of RangeError
+'writableType' => Exception raised of RangeError

Tests/LibWeb/Text/input/Streams/TransformStream-readableType-writableType-has-value.html

@@ -0,0 +1,19 @@
+<script src="../include.js"></script>
+<script>
+    test(() => {
+        try {
+            new TransformStream({
+                readableType: 'bytes',
+            });
+        } catch (e) {
+            println(`'readableType' => Exception raised of ${e.constructor.name}`);
+        }
+        try {
+            new TransformStream({
+                writableType: 'bytes',
+            });
+        } catch (e) {
+            println(`'writableType' => Exception raised of ${e.constructor.name}`);
+        }
+    });
+</script>