Automatically marshal COM outputs as WinRT

[jevansaks]

Summary

• Automatically projects recognized COM IID/void** outputs through C#/WinRT when the returned identity implements IInspectable, with COM fallback on E_NOINTERFACE.
• Enables the behavior by default and adds the comInterop.autoWinRTMarshalling opt-out.
• Supports flat P/Invoke, generated COM RCW and CCW paths, built-in COM, null output, and Native AOT.
• Returns the exact sibling-riid interface from managed COM implementations through coordinated IID and object marshallers.
• Documents the selected architecture under docs/design.

Validation

• Full warning-as-error build and package creation.
• 1,650 non-hardware tests passed.
• 68 hardware-dependent tests passed.
• Native AOT package-consumption publish and runtime validation passed.
• Adversarial COM ownership and ABI review found no defects.

Design: #1770

ADO bug: https://dev.azure.com/microsoft/OS/_workitems/edit/63185687

Generated with Copilot CLI, model: GPT-5.6 Sol.

[jevansaks]

The first hardware run exposed a test-only environment dependency: SIGDN_NORMALDISPLAY returned win on Windows Server (extensions hidden) instead of win.ini. Commit d26630d now asserts the stable SIGDN_FILESYSPATH; the focused test passes in Release on .NET 9 and .NET 10.