Add support for emscripten screen resize. (#463)

This resolves:
https://github.com/ArthurSonzogni/FTXUI/issues/432

src/ftxui/component/screen_interactive.cpp

@@ -135,6 +135,17 @@ void EventListener(std::atomic<bool>* quit, Sender<Task> out) {
   }
 }
 
+extern "C" {
+  EMSCRIPTEN_KEEPALIVE
+  void ftxui_on_resize(int columns, int rows) {
+    Terminal::SetFallbackSize({
+        columns,
+        rows,
+    });
+    std::raise(SIGWINCH);
+  }
+}
+
 #else
 #include <sys/time.h>  // for timeval
 

src/ftxui/screen/terminal.cpp

@@ -38,7 +38,10 @@ Dimensions& FallbackSize() {
   constexpr int fallback_width = 80;
   constexpr int fallback_height = 24;
 #endif
-  static Dimensions g_fallback_size{fallback_width, fallback_height};
+  static Dimensions g_fallback_size{
+      fallback_width,
+      fallback_height,
+  };
   return g_fallback_size;
 }