Update MPS doc to correct file names, commands

[pytorchbot]

Summary

There are a few updates needed to the MPS docs. I made the following changes:

• Link to the build from source docs, as the instructions on the MPS docs have to be run from the source directory.
• Update the MV3 pte file name is some of the example commands. It previously did not match the file generated from the example export.
• Update the devtools inspector command to use the devtools namespace instead of sdk, which no longer works.

Test plan

Ran through the MPS documentation page locally with the updated commands.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/12781

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❌ 3 New Failures, 27 Pending

As of commit 9cdc719 with merge base de24489 ():

NEW FAILURES - The following jobs have failed:

• Lint / lintrunner / linux-job (gh)
• pull / android / build-llm-demo / linux-job (gh)
  RuntimeError: Command docker exec -t 511f49937d8575aea6fa66b6423b92c80952b00f2d2cd3bd994a7bef3c076e2a /exec failed with exit code 2
• pull / test-eval_llama-mmlu-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 4627eb84c8458b173c237795ca683176bacceec07cd97b43d4552b29729338e6 /exec failed with exit code 1

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