Indexing/element access on super avoids instance property checks

[DanielRosenwasser]

Discovered in conversation at #55892 (comment)

class C {
    yadda = () => {};
}

class D extends C {
    badda() {
        super["yadda"]();
    }
}

new D().badda()

Currently there is no error for this code; however, if you switched it to a property access, you'd get the error introduced at #54056.

class C {
    yadda = () => {};
}

class D extends C {
    badda() {
        super.yadda(); // ❌ errors, as expected
    }
}

[Andarist]

I imagine that there are also other bugs here. checkElementAccessExpression doesn't end up checking if it's accessing on super at any layer (from what I can see quickly) and checkPropertyAccessibilityAtLocation can produce 2 other diagnostics as well (within the isSuper branch)