[ET-VK] Enable custom rotary embedding module replacement (#6424)

Pull Request resolved: https://github.com/pytorch/executorch/pull/6393

## Context

Implements a module replacement source transform to use the rotary embedding custom op introduced in the previous diff in the Llama model.
ghstack-source-id: 249175727
@exported-using-ghexport

Differential Revision: [D64697590](https://our.internmc.facebook.com/intern/diff/D64697590/)

Co-authored-by: Stephen Jia <ssjia@meta.com>