Implement myObjectAssign(target, ...sources)
Write myObjectAssign(target, ...sources) that copies the own enumerable properties of each source object onto target, in order (later sources win on key conflicts), mutates target in place, and returns it. null/undefined sources are silently skipped.
myObjectAssign({ a: 1 }, { b: 2 }, { a: 99 }); // { a: 99, b: 2 }