New port libspatialaudio

[jlskuz]

• Changes comply with the maintainer guide.
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[vicroms]

Some Copilot findings:

Upstream bundles third-party code, source/kiss_fft and source/mit_hrtf. The bundled sources should be removed before building and the meson.build script modified to accept vcpkg dependencies instead.

Optional, remove the tests from the build. Meson unconditionally adds tests and the build compiled/linked all four test executables. They are not installed, so this is not a packaging leak, but it is avoidable build work if upstream can be patched to add a test toggle.