Scopes: tweak function example and usage advice

[connor4312]

I've been catching up on some spec reading, and noticed the example in the scopes proposal. The bracketed region is the region where message -> _m is renamed in the proposal:

var _x = 1;
function _z(_m) [{
  let _y = 2;
  console.log(_m + _y);
}]
console.log("Hello World2"); // <- Inlined

Instead, it should be

var _x = 1;
function _z([_m) {
  let _y = 2;
  console.log(_m + _y);
}]
console.log("Hello World2"); // <- Inlined

since _m can be used in parameter initializers of later arguments, for example function _z(_m, _k = _m) {. Similarly in loop statements one can do stuff like for (const { a, b = a } of arr).

I suspect this may be a common problem for generators since it's not really a 'scope range' as a programmer may normally think of it, so it may be worth calling out or at least updating the example.