Support precompiling 'ComInterfaceEntry' vtables in ILC cctor interpreter (Native AOT)

[Sergio0694]

Follow-up to #114024

Opening this for tracking as suggested by @MichalStrehovsky. This is a follow up to getting ILC to support folding CCW/RCW vtables into RVA fields. We have a similar need to also get ILC to fold ComInterfaceEntry vtables, which is what we need to return to ComWrappers from the ComputeVtables method. We have hundreds (or thousands) of these, as they're needed by every single:

• User-defined type that's marshalled
• Generic type instantiation (both collections and delegate types)

We'd basically need to support this:

public struct MyTypeVtableEntries
{
    public ComInterfaceEntry IWhatever;
    public ComInterfaceEntry IStringable;
    public ComInterfaceEntry IWeakReferenceSource;
    public ComInterfaceEntry IAgileObject;
    public ComInterfaceEntry IInspectable;
    public ComInterfaceEntry IUnknown;
}

public static class MyTypeImpl
{
    [FixedAddressValueType]
    private static readonly MyTypeVtableEntries VtableEntries;

    static MyTypeImpl()
    {
        VtableEntries.IWhatever.IID = new Guid(0x1234, 0x1234, 0x1234, 0x12, 0x23, 0x34, 0x45, 0x56, 0x67, 0x78, 0x89);
        VtableEntries.IWhatever.Vtable = IWhateverImpl.Vftbl;
        VtableEntries.IStringable.IID = new Guid(0x1234, 0x1234, 0x1234, 0x12, 0x23, 0x34, 0x45, 0x56, 0x67, 0x78, 0x89);
        VtableEntries.IStringable.Vtable = IStringableImpl.AbiToProjectionVftablePtr;
        VtableEntries.IWeakReferenceSource.IID = new Guid(0x1234, 0x1234, 0x1234, 0x12, 0x23, 0x34, 0x45, 0x56, 0x67, 0x78, 0x89);
        VtableEntries.IWeakReferenceSource.Vtable = IWeakReferenceSourceImpl.AbiToProjectionVftablePtr;
        VtableEntries.IAgileObject.IID = new Guid(0x1234, 0x1234, 0x1234, 0x12, 0x23, 0x34, 0x45, 0x56, 0x67, 0x78, 0x89);
        VtableEntries.IAgileObject.Vtable = IAgileObjectImpl.AbiToProjectionVftablePtr;
        // etc...
    }
}

Where:

• All IID fields are set to constant IIDs using this constructor (Michal said it's the easiest one to fold)
• All Vtable fields are set to (nint)Unsafe.AsPointer(in Vftbl) fields, them being foldable CCW vtables from Support precompiling CCW vtables in ILC cctor interpreter (Native AOT) #114024

This doesn't need to be super general. At least on our end, we only need this to work with ComInterfaceEntry specifically (from the BCL).

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