[ET-VK] Fix embedding_q4gsw out-of-bounds access with dynamic shapes

[SS-JIA]

Stack from ghstack (oldest at bottom):

• -> [ET-VK] Fix embedding_q4gsw out-of-bounds access with dynamic shapes #18558

The embedding_q4gsw shader used push constants for num_indices,
out_height, and embed_dim that were captured at graph build time and
never updated when input tensors were dynamically resized. This caused
out-of-bounds GPU memory reads when the actual input was smaller than
the initial allocation, resulting in VK_ERROR_DEVICE_LOST on Mali GPUs.

The fix derives all shape-dependent values (embed_dim, out_height,
num_indices) from the output tensor's sizes UBO, which is automatically
updated on resize. Only truly constant values (group_size,
is_linear_weight) remain as push constants.

Root cause: With a 7-token input on a graph built for 256 tokens, the
local workgroup rounding created an extra thread (y=7) that passed the
stale bounds check (7 >= 256 == false) and read past the 7-element
indices buffer.

Differential Revision: D98642319

[pytorch-bot]

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🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/18558

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❌ 1 New Failure, 1 Cancelled Job, 2 Unrelated Failures

As of commit 33dfb14 with merge base 24751f1 ():

NEW FAILURE - The following job has failed:

• pull / android / run-emulator (gh)
  The process '/usr/bin/sh' failed with exit code 1

CANCELLED JOB - The following job was cancelled. Please retry:

• pull / unittest / macos / macos-job (gh)
  ##[error]The operation was canceled.

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / unittest / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest-editable / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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