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

backends/vulkan/test/vulkan_compute_api_test.cpp

@@ -1133,7 +1133,7 @@ TEST(
   }
 
   for (int n_idx = 0; n_idx < n; n_idx++) {
-    for (int c_idx = b_dst_offset + b_range + 1; c_idx < c; c_idx++) {
+    for (int c_idx = b_dst_offset + b_range; c_idx < c; c_idx++) {
       for (int h_idx = 0; h_idx < h; h_idx++) {
         for (int w_idx = 0; w_idx < w; w_idx++) {
           auto dst_idx = get_buf_idx(graph, out, {n_idx, c_idx, h_idx, w_idx});