Update on "[ET-VK][ez] Make squeeze insertion requirements more strict"

## Context

Refactor the `SqueezeUnsqueezeInputs` pass to be more clear about its intention.

For Llama models, input shapes to 4 bit linear will oftentimes have the shape `[1, seq_len, dim]`; under the current implementation of the pass, the input would be squeezed to `[seq_len, dim]` even though the squeeze is not necessary.

The original intention of thispass was to squeeze inputs with shape `[batch_size, 1, dim]` to `[batch_size, dim]` before calling the 4-bit linear operator.

## Changes

To avoid inserting unnecessary squeeze/unsqueezes, be more specific about when squeeze/unsqueeze should be added.

I would like to consider refactoring this pass in the future, since the logic is currently a bit uninttuitive. Squeeze/unsqueeze is also inserted for gelu and relu, but this is to create a chain of unsqueeze/squeeze that will be eliminated by a later pass (see #8601 / D69673068). I think eventually it will be good to rewrite the pass to make shape management more explicit and self contained within the pass rather than inserting ops which are expected to be removed later on.

Differential Revision: [D72480178](https://our.internmc.facebook.com/intern/diff/D72480178/)

[ghstack-poisoned]

Author: SS-JIA

backends/vulkan/_passes/squeeze_unsqueeze_inputs.py

@@ -30,6 +30,12 @@ class SqueezeUnsqueezeInputs(ExportPass):
     def should_squeeze(self, op, shape: List[int]) -> bool:
         if len(shape) == 3:
             return shape[1] == 1 and shape[0] > 1
+        if len(shape) == 4:
+            # No need to squeeze if all dims are 1 except the width dim
+            if all(dim == 1 for dim in shape[:-1]):
+                return False
+            # Otherwise, check for squeezable dim
+            return 1 in shape[:-1]
 
         # Prefer not to introduce additional orchestration ops by default
         return False