Refactor engine main loop to allow external stepping in Web

Source/Engine/Main/Web/main.cpp

@@ -3,10 +3,48 @@
 #if PLATFORM_WEB
 
 #include "Engine/Engine/Engine.h"
+#include <emscripten/emscripten.h>
+
+class PlatformMain
+{
+    int32 State = 0;
+
+    static void Loop()
+    {
+        // Tick engine
+        Engine::OnLoop();
+
+        if (Engine::ShouldExit())
+        {
+            // Exit engine
+            Engine::OnExit();
+            emscripten_cancel_main_loop();
+            emscripten_force_exit(Engine::ExitCode);
+            return;
+        }
+    }
+
+public:
+    static int32 Main()
+    {
+        // Initialize engine
+        int32 result = Engine::OnInit(TEXT(""));
+        if (result != 0)
+            return result;
+
+        // Setup main loop to be called by Emscripten
+        emscripten_set_main_loop(Loop, -1, false);
+
+        // Run the first loop
+        Loop();
+
+        return 0;
+    }
+};
 
 int main()
 {
-    return Engine::Main(TEXT(""));
+    return PlatformMain::Main();
 }
 
 #endif