False warning: pattern matching on a field doesn't count as a use

```cs
class C
{
    C field1 = null;
    public static void Main()
    {        
        _ = new C() is { field1: {} }; // CS0414 (not expected)
    }
}
```
```cs
class C
{
    C field1;
    public static void Main()
    {        
        _ = new C() is { field1: {} }; // CS0169 (not expected)
    }
}
```

Test plan: https://github.com/dotnet/roslyn/issues/52468