Windows.Foundation await adapters do not compile with C++20 standard coroutines

[kobykahane]

With cppwinrt 2.0.201008.2, the following does not compile with Visual Studio 2019 16.8 Preview 3.2 with /std:c++latest:

#include <coroutine>
#include <winrt/base.h>
#include <winrt/Windows.Foundation.h>
#include <winrt/Windows.Devices.Bluetooth.h>

using namespace winrt;

using winrt::Windows::Foundation::IAsyncOperation;

IAsyncOperation<Windows::Devices::Bluetooth::BluetoothLEDevice> foo()
{
    auto bluetoothAdapter = co_await Windows::Devices::Bluetooth::BluetoothAdapter::GetDefaultAsync();
    co_return nullptr;
}

with the error:

...Generated Files\winrt\base.h(8415,46): error C2338: Not an awaitable type
...Generated Files\winrt\base.h(8460,30): error C2039: 'await_resume': is not a member of 'winrt::Windows::Foundation::IAsyncOperation<winrt::Windows::Devices::Bluetooth::BluetoothAdapter>'

If the build is reverted to legacy coroutines by passing /await and including <experimental/coroutine> instead, the code compiles successfully.

The problem appears to be that the various co_await operators in Windows.Foundation.h have the following conditional:

#if defined(__cpp_coroutines)

which is the feature-test macro for the legacy Coroutines TS, rather than also including __cpp_lib_coroutine. Furthermore, the adapters themselves may need some adjustments, although I have not looked into that.
There appear to be a few other places that still only test for the Coroutines TS macro.