Add modules support (#1015)

Add experimental C++20 module suppport.
Co-authored-by: ArthurSonzogni <sonzogniarthur@gmail.com>

src/ftxui/screen/deprecated.cppm

@@ -0,0 +1,19 @@
+/**
+ * @file box.cppm
+ * @brief Module file for the deprecated parts of the Screen module
+ */
+
+module;
+
+#include <ftxui/screen/deprecated.hpp>
+
+export module ftxui.screen.deprecated;
+
+/**
+ * @namespace ftxui
+ * @brief The FTXUI ftxui:: namespace
+ */
+export namespace ftxui {
+    using ftxui::wchar_width;
+    using ftxui::wstring_width;
+}