Avoid unnecessary async state machine generation

[hez2010]

We have plenty of code like below:

async IAsyncOperation<T> Foo()
{
    return await AsyncInfo.Run(async () => 
    {
        // no await in the body at all
        return foo;
    });
}

which doesn't actually await anything in an async method. Instead, we should rewrite them to

IAsyncOperation<T> Foo()
{
    return Task.FromResult(foo).AsAsyncOperation();
}

This can avoid unnecessary async state machine be generated to reduce GC pressure.

[QuaintMako]

Linking it the performance issues maybe? Anyone taking up that issue may want to dive deeper into optimization.

[QuaintMako]

I believe there is no longer any return await AsyncInfo.Run methods inside the codebase.

Does this issue also concerns any return AsyncInfo.Run that does not have any await in its instructions?