Implement changes for "avoid mostly-redundant `await` in async `yield*`"

[bakkot]

These are updates for https://github.com/tc39/ecma262/pull/2819.

I made the relevant modification to engine262 in a local branch, ran all of test262, and only found one test whose behavior needed to change, which was exercising the number of ticks implied by yield* in an async generator. This PR modifies that test and also adds an explicit test for that yield* does not perform unwrapping of the inner value.

I recommend reviewing commits individually - in particular, the first commit only updates the existing test's info to match the current spec, which is then modified to match https://github.com/tc39/ecma262/pull/2819 in the second commit. It's hard to see the change otherwise.

cc @anba who wrote the test which is being updated.