Issues with 'keyof' in 'for-in' statements and 'in' operator #12513

function f1<K extends string, T>(obj: { [P in K]: T }, k: K) {
    const b = k in obj;    // Error
    let k1: K;
    for (k1 in obj) {      // Error
        let x1 = obj[k1];  // Error
    }
    for (let k2 in obj) {
        let x2 = obj[k2];  // Error
    }
}

function f2<T>(obj: { [P in keyof T]: T[P] }, k: keyof T) {
    const b = k in obj;
    let k1: keyof T;
    for (k1 in obj) {
        let x1 = obj[k1];
    }
    for (let k2 in obj) {
        let x2 = obj[k2];
    }
}

function f3<T, K extends keyof T>(obj: { [P in K]: T[P] }, k: K) {
    const b = k in obj;    // Error
    let k1: K;
    for (k1 in obj) {      // Error
        let x1 = obj[k1];
    }
    for (let k2 in obj) {
        let x2 = obj[k2];  // Error
    }
}