Update base for Update on "[ET-VK][11/n] copy_channel_offsets node"

1. Add a node `copy_channel_offsets` specifically for copying along the channel dimension, it needs extra attention at the boundaries due to channel packing.
1.1. `copy_channel_offsets` will be useful for `aten.cat` and `aten.split`.
2. Create `etvk.*` operators to facilitate testing. Add test case for both `copy_offset` and `copy_channel_offset`.

Differential Revision: [D56554426](https://our.internmc.facebook.com/intern/diff/D56554426/)

[ghstack-poisoned]

Author: yipjustin