metadata: Add audiopolicy.h

[riverar]

Adds audiopolicy interfaces and types. Is compatible with #4700.

[kennykerr]

Prefer appending headers to the end of the list unless there is a good reason to add it in some specific order.

[riverar]

Fair, though note there's these comment blocks at the end of the array which suggests they should be last. (I'm guessing I can ignore that.)

...
    // Apiset umbrella fallback (appended last). Modern APIs that no per-DLL host library
    // claims — `CreateFileMapping2`, the `*FromApp` file APIs, the package-dependency APIs,
    // … — are exported only through an `api-ms-win-*` apiset contract (or a host DLL the
    // umbrella records). Because resolution is first-wins and these come last, every
    // classic host-DLL mapping above is untouched; only the previously-empty residue is
    // stamped with the faithful DLL the umbrella records, matching the reference metadata,
    // which likewise leaves no function with an empty library.
    "onecore.lib",
    "onecoreuap.lib",
    // Enclave runtime, resolved dead last. `vertdll.dll` is the VBS-enclave runtime and
    // also exports host-side synchronization/enclave functions (`WaitOnAddress`,
    // `WakeByAddress*`, `CallEnclave`, `TerminateEnclave`); importing those from
    // `vertdll.dll` faults a normal process at load. Placing it after the apiset umbrella
    // lets those functions resolve to their loadable `api-ms-win-*` contract first, leaving
    // `vertdll.lib` to stamp only genuinely enclave-only residue (`EnclaveSealData`, …).
    "vertdll.lib",
];

[kennykerr]

I meant the end of the header list not the lib list. Yes, I'd stick any specific lib at the end but before the umbrella libs.