[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/BackendObject.h

@@ -113,6 +113,10 @@ namespace MobileGL {
         struct DynamicBackendParameters {
             SizeT UniformBufferOffsetAlignment = 256;
             SizeT MaxShaderStorageBlockSize = 128 * 1024 * 1024;
+            Uint32 SubgroupSize = 0;
+            Uint32 SubgroupSupportedStages = 0;
+            Uint32 SubgroupSupportedFeatures = 0;
+            Bool SubgroupQuadOperationsInAllStages = false;
         };
 
         enum class WindowBackend {