Implementing only a setter is enough to implement a getter

[weswigham]

And vice-versa.

Inspired by #33621

Code

declare class Properties {
    set val(x: number);
}

class BadProps implements Properties {
    private _val: number = 42;
    get val() {
        return this._val;
    }
}

declare class Properties2 {
    get val(): number;
}

class BadProps2 implements Properties2 {
    private _val: number = 42;
    set val(x: number) {
        this._val = 2;
    }
}

const x: Properties = new BadProps();
x.val;
x.val = 12;

const x2: Properties2 = new BadProps2();
x2.val;
x2.val = 12;

Expected behavior:
Error on BarProps for incorrectly implementing Properties.
Error on BarProps2 for incorrectly implementing Properties2.

Actual behavior:
No error, even with "useDefineForClassFields": true.

[RyanCavanaugh]

We have eleventydozen issues on this already; let's reopen an existing one if we want to change how it works.