[ExecuTorch][WebGPU] Shared pipeline + dispatch-grid + vec4-align helpers (op-suite foundation) (#21243)

This PR was created by the merge bot to help merge the original PR into
the main branch.
ghstack PR number: https://github.com/pytorch/executorch/pull/20842 by
@JCNTH
^ Please use this as the source of truth for the PR details, comments,
and reviews
ghstack PR base:
https://github.com/pytorch/executorch/tree/gh/JCNTH/17/base
ghstack PR head:
https://github.com/pytorch/executorch/tree/gh/JCNTH/17/head
Merge bot PR base: https://github.com/pytorch/executorch/tree/main
Merge bot PR head:
https://github.com/pytorch/executorch/tree/gh/JCNTH/17/orig

@diff-train-skip-merge

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Co-authored-by: Julian Ng-Thow-Hing <juliannth@meta.com>