[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/Renderer/VulkanRenderer.h

@@ -143,6 +143,7 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         void DispatchCompute(GLuint numGroupsX, GLuint numGroupsY, GLuint numGroupsZ);
         void DispatchComputeIndirect(GLintptr indirect);
         void MemoryBarrier(GLbitfield barriers);
+        static VkMemoryBarrier BuildMemoryBarrierForGlBarriers(GLbitfield barriers);
         void DrawArrays(const DrawCmd& payload);
         void DrawElements(const DrawIndexedCmd& payload);
         void MultiDrawElements(const MultiDrawIndexedCmd& payloads);
@@ -151,6 +152,7 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         void Present();
 
         const PhysicalDevice& GetPhysicalDevice() const;
+        VkInstance GetInstance() const;
         Bool IsDrawIndirectCountExtensionEnabled() const;
 
         void RecreateSwapchain();