[Codegen] Support dynamic dimensions in collapse_shape into interface store folding

[jtuyls]

Towards: https://github.com/iree-org/iree/issues/20835

Supporting dynamic dimensions in the tensor.collapse_shape into iree_tensor_ext.dispatch.tensor.store folding is needed to support pad encodings in e2e Llama3 as the remaining collapses will otherwise result in linalg.copy operations on workspace and global memory (which results in a compilation failure).