[WebGPU] GPUAutoLayout should have special designation

Currently it is created like so:

    m_autoPipelineLayout(createPipelineLayout({ { "autoLayout"_s, }, { } }))

and relies on the fact that the implementation of PipelineLayout::isValid is:

    bool isValid() const { return !m_bindGroupLayouts.isEmpty(); }

however a pipeline layout may have zero bind group layouts. So we need a special designation for auto layout.