Add support for italics (#1009)

Co-authored-by: Ken Reneris <ms/devops kreneris@microsoft.com>
Co-authored-by: ArthurSonzogni <sonzogniarthur@gmail.com>

src/ftxui/dom/italic_test.cpp

@@ -0,0 +1,22 @@
+// Copyright 2025 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.
+#include <string>  // for allocator, string
+
+#include "ftxui/dom/elements.hpp"   // for operator|, text, bold, Element
+#include "ftxui/dom/node.hpp"       // for Render
+#include "ftxui/screen/screen.hpp"  // for Screen, Pixel
+#include "gtest/gtest.h"  // for Test, AssertionResult, EXPECT_TRUE, Message, TEST, TestPartResult
+
+// NOLINTBEGIN
+namespace ftxui {
+
+TEST(ItalicTest, Basic) {
+  auto element = text("text") | italic;
+  Screen screen(5, 1);
+  Render(screen, element);
+  EXPECT_TRUE(screen.PixelAt(0, 0).italic);
+}
+
+}  // namespace ftxui
+// NOLINTEND