StyledText: add a generator test and fix C++ compilation

api/cpp/cbindgen.rs

@@ -302,6 +302,7 @@ fn gen_corelib(
         "SwipeGestureHandler",
         "Flickable",
         "SimpleText",
+        "StyledTextItem",
         "ComplexText",
         "Path",
         "WindowItem",

tests/cases/elements/styledtext.slint

@@ -0,0 +1,26 @@
+// Copyright © SixtyFPS GmbH <[email protected]>
+// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-Royalty-free-2.0 OR LicenseRef-Slint-Software-3.0
+
+export component TestCase inherits Window {
+
+    st := StyledText {
+        text: @markdown("Hello **World**: {}", "_abc_");
+        font-size: 24px;
+        color: red;
+    }
+
+    out property <bool> test: true;
+}
+
+/*
+```rust
+let instance = TestCase::new().unwrap();
+assert!(instance.get_test());
+```
+
+```cpp
+auto handle = TestCase::create();
+const TestCase &instance = *handle;
+assert(instance.get_test());
+```
+*/