Per-iteration scoped variables not emitted per-iteration when using for..await

[rbuckton]

I found a similar case: constants with scope inside a for await are compiled outside __generator and so are shared across iterations.

const sleep = (tm: number) => new Promise(resolve => setTimeout(resolve, tm));

async function* gen() {
    yield 1;
    await sleep(1000);
    yield 2;
}

const log = console.log;

(async () => {
    for await (const outer of gen()) {
        log(`I'm loop ${outer}`);
        (async () => {
            const inner = outer;
            await sleep(2000);
            if (inner === outer) {
                log(`I'm loop ${inner} and I know I'm loop ${outer}`);
            } else {
                log(`I'm loop ${inner}, but I think I'm loop ${outer}`);
            }
        })();
    }
})();

Using es5 target, it prints:

[LOG]: I'm loop 1 
[LOG]: I'm loop 2 
[LOG]: I'm loop 1, but I think I'm loop 2 
[LOG]: I'm loop 2 and I know I'm loop 2 

Using ES2015 or following, it prints (as expected):

[LOG]: I'm loop 1 
[LOG]: I'm loop 2 
[LOG]: I'm loop 1 and I know I'm loop 1 
[LOG]: I'm loop 2 and I know I'm loop 2 

I was able to replicate it on the playground with version 4.0.1 and older 3.x.x versions.

Originally posted by @dippi in #40047 (comment)