[ET-VK] Replacing use of adaptive_work_group_size function by create_local_wg_size function.

Pull Request resolved: https://github.com/pytorch/executorch/pull/7016

This diff replaces the use of the adaptive_work_group_size function with create_local_wg_size function for slice and copy ops, which is better tuned for improving shader performance.
ghstack-source-id: 256728327
@exported-using-ghexport

Differential Revision: [D66308779](https://our.internmc.facebook.com/intern/diff/D66308779/)

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Co-authored-by: Vivek Trivedi <5340687+trivedivivek@users.noreply.github.com>