Suggestion: strict mode should detect yield-returning inside a lock

[WizardBrony]

For example, the following code fails:

public class C
{
    private readonly object _lock = new object();

    public IEnumerable<int> Iterator()
    {
        lock (_lock)
            yield return 0;
    }
}

var c = new C();
foreach (var i in c.Iterator())
    await Task.Yield();

The compiler should generate an error (or at least a warning) informing the user that the currently-executing thread after yield-returning may not be the same thread that the lock was taken on. Considering that the compiler already prevents awaiting in the body of a lock statement (Error CS1996) for the same reason, I feel like this addition would follow suit.

[jcouv]

Tagging @JJones. I think we can close this now as LDM discussed this and concluded that yield return should be allowed in a lock as it is in a try/finally.
See #74024 for context