feat(lwjgl3): add Vulkan renderer backend

Port of the Dear ImGui Vulkan renderer (imgui_impl_vulkan) into the
imgui-lwjgl3 module:
- ImGuiImplVulkan renderer with descriptor sets, pipeline creation and
  font atlas upload; shader SPIR-V shipped as classpath resources
- ImGuiImplVulkanH helper structures
- createVulkanSurface() helpers for the GLFW and SDL3 backends
- imgui-app: VULKAN backend with WindowVulkan (swapchain, render pass,
  per-frame sync objects and resize handling)
- example: ExampleVulkan smoke test

Co-authored-by: DeepSeek <noreply@deepseek.com>

Author: Enaium

example/src/main/java/ExampleVulkan.java

@@ -0,0 +1,29 @@
+import imgui.ImGui;
+import imgui.app.Application;
+import imgui.app.Backend;
+import imgui.app.Configuration;
+
+/**
+ * Smoke-test entry point for the Vulkan backend. Run with:
+ * <pre>
+ * ./gradlew :example:run -PmainClass=ExampleVulkan
+ * </pre>
+ */
+public class ExampleVulkan extends Application {
+    @Override
+    protected void configure(final Configuration config) {
+        config.setTitle("Example Application — Vulkan");
+        config.setBackend(Backend.VULKAN);
+    }
+
+    @Override
+    public void process() {
+        ImGui.begin("Vulkan");
+        ImGui.text("Hello from the Vulkan backend!");
+        ImGui.end();
+    }
+
+    public static void main(final String[] args) {
+        launch(new ExampleVulkan());
+    }
+}

imgui-app/build.gradle

@@ -23,6 +23,7 @@ dependencies {
     api 'org.lwjgl:lwjgl-glfw'
     api 'org.lwjgl:lwjgl-opengl'
     api 'org.lwjgl:lwjgl-sdl'
+    api 'org.lwjgl:lwjgl-vulkan'
 
     ['natives-linux', 'natives-windows', 'natives-macos', 'natives-macos-arm64'].each {
         api "org.lwjgl:lwjgl::$it"

imgui-app/src/main/java/imgui/app/Application.java

@@ -134,7 +134,18 @@ public final Color getColorBg() {
     public static void launch(final Application app) {
         final Configuration config = new Configuration();
         app.configure(config);
-        app.window = (config.getBackend() == Backend.SDL) ? new WindowSdl() : new WindowGlfw();
+        switch (config.getBackend()) {
+            case SDL:
+                app.window = new WindowSdl();
+                break;
+            case VULKAN:
+                app.window = new WindowVulkan();
+                break;
+            case GLFW:
+            default:
+                app.window = new WindowGlfw();
+                break;
+        }
         app.window.setOwner(app);
         app.window.init(config);
         app.preRun();

imgui-app/src/main/java/imgui/app/Backend.java

@@ -11,5 +11,9 @@ public enum Backend {
     /**
      * SDL3 platform + SDL_GPU renderer.
      */
-    SDL
+    SDL,
+    /**
+     * GLFW platform + Vulkan renderer.
+     */
+    VULKAN
 }