[Fix] (MG_Backend/DirectVulkan): fix Voxy subgroup and indirect draw sync

- Implement Vulkan subgroup capability querying and expose KHR subgroup getter values.

- Fix DirectVulkan memory barriers so GL_COMMAND_BARRIER_BIT makes generated indirect draw commands visible.

- Keep Voxy on the DirectVulkan gpu_shader_int64 quad decode path while filtering unsupported optional int64 usage on backends that do not advertise it.

- Add MG_Test coverage for subgroup getters, Voxy subgroup/int64 shader probes, command barrier mapping, and indirect draw command layout.

- Check for whether driver supports shader subgroup operation, disable on demand, and provide env var `MOBILEGL_DISABLE_SUBGROUP` to explicitly disable subgroup features

MobileGL/MG_Backend/DirectVulkan/BackendObject_DirectVulkan.h

@@ -14,6 +14,7 @@
 namespace MobileGL::MG_Backend::DirectVulkan {
     class BackendObject_DirectVulkan : public BackendObject {
     public:
+        BackendObject_DirectVulkan();
         ~BackendObject_DirectVulkan() override;
 
         void Initialize() override;
@@ -30,12 +31,15 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         const GlobalBackendFunctionsTable& GetBackendFunctions() const override;
         const DynamicBackendParameters& GetDynamicParameters() const override;
         BackendType GetBackendType() const override;
+        void ApplyVulkanCapabilitiesForTesting(const MG_External::VulkanCapabilities& capabilities);
 
     private:
+        void UpdateAdvertisedExtensions();
         void UpdateDynamicBackendParameters();
 
         Bool m_initialized = false;
         DynamicBackendParameters m_dynamicParameters;
         MG_External::VulkanCapabilities m_vulkanCaps;
+        RendererInfo m_rendererInfo;
     };
 } // namespace MobileGL::MG_Backend::DirectVulkan