New analyzer: [MustBeLocked] attribute to ensure all callers lock an argument before invoking a method

[ronnygunawan]

class Foo {
    private object? _obj = null;
    private readonly ConcurrentDictionary<int, object> _dictionary = new();

    void M() {
        if (_dictionary.TryGetValue(100, out object? obj)) {
            N(obj); // warning: obj must be locked before calling this method
            
            lock (obj) {
                N(obj); // no warning
            }
        }
    }
    
    void N([MustBeLocked] object x) {
        if (x is List<int> list) {
            list.Add(0);
        }
    }
}