anv/pipeline: Constant fold after apply_pipeline_layout

Thanks to the new NIR load_descriptor intrinsic added by the UBO/SSBO lowering series, we weren't getting UBO pushing because the UBO range detection pass couldn't see the constants it needed. This fixes that problem with a quick round of constant folding. Because we're folding we no longer need to go out of our way to generate constants when we lower the vulkan_resource_index intrinsic and we can make it a bit simpler.