This MR adds a very basic implementation of `IPropertyDescription` for system defined properties (i.e, the ones in <propkey.h>). This is needed to support the [`Properties`](https://learn.microsoft.com/en-us/uwp/api/windows.devices.enumeration.device...) method for `IDeviceInformation` in Windows.Devices.Enumeration (!6874).
-- v8: propsys: Implement IPropertyDescription for several known system properties. propsys: Add IPropertyDescription stub for system defined properties. propsys/tests: Add conformance tests for PSGetNameFromPropertyKey. propsys: Add stubs for PSGetNameFromPropertyKey. propsys: Add stubs for PropertySystem. propsys/tests: Add conformance tests for PSGetPropertyKeyFromName. propsys/tests: Add conformance tests for getting PropertyDescriptions from PropertySystem.