New Feature Requesting for `const` Parameter

I have a small new feature to request. Let say we have this piece of code:

function setButton(button: Button | undefined) {
    if (button) {
        button.onclick = () => {
            // tsc complains button might be undefined(well done!), 
            // because it might be set to undefined later on,
            // as you can see below `button = undefined;`. 
            button.setAttribute('disabled', 'true'); //error
        }
    }
    // some other code goes here...
    // and eventually, button is set to undefined.
    button = undefined;
}

Fortunately, there is a way to fix this:

function setButton(button: Button | undefined) {
    const constButton = button;
    if (constButton) {
        constButton.onclick = () => {
            // now tsc is satisfied.
            constButton.setAttribute('disabled', 'true'); 
        }
    }
    
    // impossible to assign to a const variable.
    // constButton = undefined;
}

But can we twist the code a little bit, which is what I asking for? Something like this:

function setButton(const button: Button | undefined) {
    if (button) {
        button.onclick = () => {
            button.setAttribute('disabled', 'true'); 
        }
    }
}

So you can see there really are some cases a const parameter might come to handy. Thank you.

P.S. Just for demonstrating the point, here's a full demo:

class Button {
    onclick?: () => void;
    performClick() {
        if (this.onclick) this.onclick();
    }
    setAttribute(key: string, value: string) {
        //set attribute to this button
    }
}

function setButton(button: Button | undefined) {
    if (button) {
        button.onclick = () => {
            button.setAttribute('disabled', 'true');
        }
    }
    button = undefined;
}

const button = new Button();
setButton(button);
button.performClick();

Comienza reproduciendo los ejemplos de TypeScript del issue y revisando cómo las declaraciones de parámetros y el estrechamiento mediante el flujo de control gestionan las reasignaciones. Define la semántica y la sintaxis aceptadas para un parámetro const y, después, verifica que el ejemplo de callback pase el type-check, mientras que una reasignación sea rechazada.