Add buffer and image binding to QSSGRhiShaderPipeline

Adds buffer and image bindings to the pipeline. This makes it possible
for the effects and custom materials that have distributed binding
handling to set the bindings easily.

One first adds the image/buffer bindings to the pipeline, then
applies the bindings to the QSSGRhiShaderResourceBindingList at a
convenient location.

Also reads storage buffers from the shader description.

Also renames bindingForImage to bindingForStorageImage to match the
sibling.

Task-number: QTBUG-146226
Change-Id: I410a8d2c4324dd8380f34aa957bf5be4476aa335
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>