GPU: Python: Raise error when creating shaders without create info

This is adding a hard error for backends do that do not supports it.
Even without this, the backend would return a nullptr. But the error
message in this case was just "see console for more details" without
any additional detail. Which was confusing.

source/blender/python/gpu/gpu_py_shader.cc

@@ -13,6 +13,7 @@
 
 #include "BLI_utildefines.h"
 
+#include "GPU_context.hh"
 #include "GPU_shader.hh"
 #include "GPU_texture.hh"
 #include "GPU_uniform_buffer.hh"
@@ -109,6 +110,20 @@ static PyObject *pygpu_shader__tp_new(PyTypeObject * /*type*/, PyObject *args, P
 {
   BPYGPU_IS_INIT_OR_ERROR_OBJ;
 
+  if (GPU_backend_get_type() == GPU_BACKEND_VULKAN) {
+    PyErr_SetString(PyExc_Exception,
+                    "Direct shader creation is not supported on Vulkan. "
+                    "Use gpu.shader.create_from_info(shader_info) instead.");
+    return nullptr;
+  }
+
+  if (GPU_backend_get_type() == GPU_BACKEND_METAL) {
+    PyErr_SetString(PyExc_Exception,
+                    "Direct shader creation is not supported on Metal. "
+                    "Use gpu.shader.create_from_info(shader_info) instead.");
+    return nullptr;
+  }
+
   PyErr_WarnEx(PyExc_DeprecationWarning,
                "Direct shader creation is deprecated. "
                "Use gpu.shader.create_from_info(shader_info) instead.",