Add VCPKG port for C++ package management

[Copilot]

Summary

Adds VCPKG port configuration to enable C++ package management integration. Users can now install ExecuTorch via vcpkg install executorch alongside traditional pip installation.

Port structure (ports/executorch/):

• vcpkg.json - Manifest with 10 optional features (xnnpack, coreml, mps, vulkan, qnn, portable-ops, optimized-ops, quantized-ops, pybind, tests)
• portfile.cmake - CMake-based build script using vcpkg_from_github, feature-conditional configuration, and standard install patterns
• usage - CMake integration examples and target documentation
• ../README.md - Maintenance guide for registry submission and version updates

Usage:

# Install core runtime
vcpkg install executorch

# Install with features
vcpkg install executorch[portable-ops,xnnpack]

find_package(ExecuTorch CONFIG REQUIRED)
target_link_libraries(main PRIVATE executorch extension_module portable_ops_lib)

Static linkage only. SHA512 hash placeholder (0) requires update on first build. No modifications to existing build system.

Test plan

Manual verification of port file structure and CMake configuration logic. Code review and CodeQL passed with no issues. Actual VCPKG installation testing requires copying port to VCPKG installation directory and updating SHA512 hash.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Create VCPKG port</issue_title>
<issue_description>### 🚀 The feature, motivation and pitch

For better integration into my projects, I would like to use an official VCPKG port. It brings the benefits of easier installation and updating of the package.
For example, some people working on a project use the library on different devices, then a quick setup of vcpkg (most times integrated into IDE, so effectivly no setup) is only needed to get the correct version. That is exactly my case and why I would like such a port.

If not wanted, please tell me. I will then close this issue.

If anyone is interested to do this, 2 steps need to be executed.
I would also create the port, though I am not experienced.

If a port is created, someone, possibly me, would have to do updates every time a new release is out.

https://learn.microsoft.com/de-de/vcpkg/get_started/get-started-packaging
https://learn.microsoft.com/de-de/vcpkg/get_started/get-started-adding-to-registry

Alternatives

No response

Additional context

No response

RFC (Optional)

No response</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Create VCPKG port #16685

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[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/16713

• 📄 Preview Python docs built from this PR

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