Add modules support (#1015)

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

src/ftxui/ftxui.cppm

@@ -0,0 +1,11 @@
+/**
+ * @file ftxui.cppm
+ * @brief Module file re-exporting all FTXUI submodules.
+ */
+
+export module ftxui;
+
+export import ftxui.component;
+export import ftxui.dom;
+export import ftxui.screen;
+export import ftxui.util;