move menu pages loader to Lua & add gui.load_document, file.ext(), file.prefix() & add core:gui_util module

src/logic/scripting/scripting_hud.cpp

@@ -4,6 +4,7 @@
 #include "engine/Engine.hpp"
 #include "files/files.hpp"
 #include "frontend/hud.hpp"
+#include "frontend/UiDocument.hpp"
 #include "graphics/render/WorldRenderer.hpp"
 #include "objects/Player.hpp"
 #include "lua/libs/api_lua.hpp"
@@ -93,3 +94,15 @@ void scripting::load_hud_script(
     register_event(env, "on_hud_render", packid + ":.hudrender");
     register_event(env, "on_hud_close", packid + ":.hudclose");
 }
+
+gui::PageLoaderFunc scripting::create_page_loader() {
+    auto L = lua::get_main_state();
+    if (lua::getglobal(L, "__vc_page_loader")) {
+        auto func = lua::create_lambda(L);
+        return [func](const std::string& name) -> std::shared_ptr<gui::UINode> {
+            auto docname = func({name}).asString();
+            return engine->getAssets()->require<UiDocument>(docname).getRoot();
+        };
+    }
+    return nullptr;
+}