Media Foundation definitions are missing [Optional] attribute annotations (not honoring __RPC__in_opt annotation)

For example `mfobjects.h` defines this:

IMFMediaEventGenerator : public IUnknown
{
// omitted ....

virtual HRESULT STDMETHODCALLTYPE QueueEvent(
/* [in] */ MediaEventType met,
/* [in] */ __RPC__in REFGUID guidExtendedType,
/* [in] */ HRESULT hrStatus,
/* [unique][in] */ __RPC__in_opt const PROPVARIANT *pvValue) = 0; // this is an optional pointer (can be null)
};

While medatada contains this, where `pvValue `is not marked with `[Optional]` attribute:

unsafe HRESULT QueueEvent(
[In] uint met,
[In][Const] Guid* guidExtendedType, // this is OK
[In] HRESULT hrStatus,
[In][Const] PROPVARIANT* pvValue // this is not OK
);

Another example in `mfidl.h`:

IMFMediaSource : public IMFMediaEventGenerator
{
// omitted ....

virtual HRESULT STDMETHODCALLTYPE Start(
/* [in] */ __RPC__in_opt IMFPresentationDescriptor *pPresentationDescriptor,
/* [unique][in] */ __RPC__in_opt const GUID *pguidTimeFormat,
/* [unique][in] */ __RPC__in_opt const PROPVARIANT *pvarStartPosition) = 0;

In metadata:

unsafe HRESULT Start(
[In] IMFPresentationDescriptor pPresentationDescriptor,
[In][Const] Guid* pguidTimeFormat, // this is not OK
[In][Const] PROPVARIANT* pvarStartPosition // this is not OK
);

There are other places in win32metada where it's correct, for example `IAudioClient`'s `Initialize` method where AudioSessionGuid is marked with `[Optional]`:

unsafe HRESULT Initialize(
[In] AUDCLNT_SHAREMODE ShareMode,
[In] uint StreamFlags,
[In] long hnsBufferDuration,
[In] long hnsPeriodicity,
[In][Const] WAVEFORMATEX* pFormat,
[Optional][In][Const] Guid* AudioSessionGuid // this is OK
);

Compare the declarations in mfobjects.h and mfidl.h with the generated metadata, focusing on parameters marked __RPC__in_opt and the existing AudioSessionGuid example. Trace the metadata generation entry point that maps these annotations to [Optional], then verify that optional pointers in the affected Media Foundation methods are annotated consistently.

Written by the indexing model from the issue text.