Allow this typing and type parameters on static methods

[tinganho]

Since constructor visibility #2341 got merged. I haven't been able to utilise it fully because the classes I can benefit from requires type parameters and this typings on static methods.

abstract class Model<P> {
    static create(props: P): this {
        let model = window.store[this.name + props.id];
        if (model) {
            return model;
        }
        return window.store[this.name + props.id] = new this(props)
    }

    protected constructor(props: P) {
    }
}

The Model class is a base class. A this typing would be very good to refer to the subclass instead of the base class. Since many classes has type arguments in their constructors, it makes sense to allow type arguments in static factory methods as well, otherwise you cannot create type safe factory methods.

[tinganho]

Also since the original reason to allow visibility on constructors was to support static factory methods. So at least this typing on static methods needs to be supported to conform to the original reason.

[mhegazy]

duplicate of #5863