PyGPU: GPUShader: implementation of 'attrs_info_get' method

With the new `attrs_info_get` method, we can get information about
the attributes used in a `GPUShader` and thus have more freedom in the
automatic creation of `GPUVertFormat`s

Reviewed By: fclem, campbellbarton

Differential Revision: https://developer.blender.org/D15764

source/blender/python/gpu/gpu_py_shader_create_info.cc

@@ -58,7 +58,7 @@ static const struct PyC_FlagSet pygpu_qualifiers[] = {
   "      - ``IVEC3``\n" \
   "      - ``IVEC4``\n" \
   "      - ``BOOL``\n"
-static const struct PyC_StringEnumItems pygpu_attrtype_items[] = {
+const struct PyC_StringEnumItems pygpu_attrtype_items[] = {
     {(int)Type::FLOAT, "FLOAT"},
     {(int)Type::VEC2, "VEC2"},
     {(int)Type::VEC3, "VEC3"},