[Feat] (Diligent, CMake): enable DiligentCore and add initial Diligent/Vulkan backend skeleton

- Add MOBILEGL_ENABLE_DILIGENT option; build DiligentCore Vulkan-only after
  MobileGL's existing 3rdparty targets so shared glslang/SPIRV-Cross/xxHash
  targets are reused instead of duplicated.
- Add BackendType::DiligentVulkan, config parsing, and backend-object switch.
- Add DiligentBackend::BackendObject_Diligent skeleton: creates a Diligent
  Vulkan device/context when an adapter is available, advertises GL 3.2 core,
  and returns an empty GL function table for now.
- Add local DiligentVulkanSanityTest that compiles/runs on the host (skips
  device creation gracefully when no Vulkan adapter is present).
- Fix GLXImpl EGLDisplay member shadowing the X11 Display typedef, exposed by
  GCC 16 + Diligent header include order.

.gitignore

@@ -1,4 +1,4 @@
-################################################################################
+################################################################################
 # 此 .gitignore 文件已由 Microsoft(R) Visual Studio 自动创建。
 ################################################################################
 
@@ -16,6 +16,9 @@ MobileGLCodeManager
 MobileGL/MG_Test/build
 /build_*
 /cmake-build*
+/build-*/
+/local.properties
+/.jspace/
 .idea
 MobileGL/MG*/build*
 MobileGL/MG*/cmake-build*