[GPU] Add metal to DispatchKeySet

[xta0]

Stack from ghstack:

• [Metal] Add the Python binding for optimize_for_mobile #46456 [Metal] Add the Python binding for optimize_for_mobile
• [Metal] Enable optimize_for_mobile on Linux  #46384 [Metal] Enable optimize_for_mobile on Linux
• [GPU] Introduce USE_PYTORCH_METAL #46383 [GPU] Introduce USE_PYTORCH_METAL
• [GPU] Add metal to DispatchKeySet #46455 [GPU] Add metal to DispatchKeySet

After this PR(#46236 ) landed, the aten::copy_ can no longer be dispatched to Metal kernels.

Differential Revision: D24356769

[facebook-github-bot]

💊 CI failures summary and remediations

As of commit e40e4c8 (more details on the Dr. CI page):

---

• 1/1 failures possibly* introduced in this PR
  • 1/1 non-CircleCI failure(s)---

Extra GitHub checks: 1 failed

• Failed: GitHub Actions - flake8-py3

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This comment has been revised 3 times.

[dr-ci]

💊 CI failures summary and remediations

As of commit ead5860 (more details on the Dr. CI page):

---

• 2/2 failures introduced in this PR---

2 failures not recognized by patterns:

Job	Step	Action
pytorch_linux_xenial_py3_clang7_onnx_ort_test2	Run tests	🔁 rerun
pytorch_linux_xenial_py3_clang7_onnx_ort_test1	Run tests	🔁 rerun

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This comment has been revised 5 times.

[codecov]

Codecov Report

Merging #46455 into gh/xta0/57/base will decrease coverage by 0.00%.
The diff coverage is n/a.

@@                 Coverage Diff                 @@
##           gh/xta0/57/base   #46455      +/-   ##
===================================================
- Coverage            68.38%   68.38%   -0.01%     
===================================================
  Files                  411      411              
  Lines                53953    53953              
===================================================
- Hits                 36897    36896       -1     
- Misses               17056    17057       +1     

Impacted Files	Coverage Δ
torch/testing/_internal/expecttest.py	77.55% <0.00%> (-1.03%)	⬇️

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[facebook-github-bot]

This pull request has been merged in 5da4a08.