[hnswlib] new port

[moritz-h]

• Changes comply with the maintainer guide
• The name of the port matches an existing name for this component on https://repology.org/ if possible, and/or is strongly associated with that component on search engines.
• Optional dependencies are resolved in exactly one way. For example, if the component is built with CMake, all find_package calls are REQUIRED, are satisfied by vcpkg.json's declared dependencies, or disabled with CMAKE_DISABLE_FIND_PACKAGE_Xxx
• The versioning scheme in vcpkg.json matches what upstream says.
• The license declaration in vcpkg.json matches what upstream says.
• The installed as the "copyright" file matches what upstream says.
• The source code of the component installed comes from an authoritative source.
• The generated "usage text" is accurate. See adding-usage for context.
• The version database is fixed by rerunning ./vcpkg x-add-version --all and committing the result.
• Only one version is in the new port's versions file.
• Only one version is added to each modified port's versions file.

[jimwang118]

Is this port head-only? If so, only the usage of find_path() is reserved in usage.

[moritz-h]

@jimwang118 Yes it is header only, I removed the unofficial CMake target.

Maybe as follow up question for the next port: If I have a header only library, but depending on this one, should I also only use find_path() and tell in the usage file, that the user must do and additional find_path for the dependency of the library, or would it in that case be ok to add an unofficial CMake target to manage dependencies automatically?

[dg0yt]

Unofficial config should normally be avoided because it comes with a lock-in effect for users and for vcpkg. But there are situations where it can be useful enough even for header-only ports.

[jimwang118]

Tested usage successfully by the hnswlib:x64-windows triplet.